Organization	6 Months Ended
Jun. 30, 2013
Accounting Policies [Abstract]
Organization	1. Organization *Description of Business* Prothena Corporation plc (“Prothena,” the “Company,” “we,” “our” or “us”), a public limited company incorporated in Ireland, is a clinical stage biotechnology company focused on the discovery and development of novel antibodies for the potential treatment of a broad range of diseases that involve protein misfolding or cell adhesion. The Company is focused on the discovery and development of potential therapeutic monoclonal antibodies directed specifically to disease causing proteins. These potential therapies have a broad range of indications including AL and AA forms of amyloidosis (NEOD001), Parkinson’s disease and related synucleinopathies (PRX002) and autoimmune diseases and metastatic cancers (PRX003). The Company has initiated a Phase 1 clinical trial for NEOD001 with the first patient dosing in April 2013. The Phase 1 clinical trial of NEOD001 will evaluate safety and tolerability in AL Amyloidosis patients. The Company’s strategy is to identify antibody candidates for clinical development by applying its extensive expertise in generating novel therapeutic antibodies and working with collaborators having expertise in specific animal models of disease. Prothena’s business consists of a substantial portion of Elan Corporation plc’s (“Elan”) former drug discovery business platform, including Neotope Biosciences Limited (and its wholly-owned subsidiary Prothena Biosciences Inc) and Onclave Therapeutics Limited, each former wholly-owned subsidiaries of Elan (which for the period prior to separation and distribution are referred to herein as the “Prothena Business”). Effective December 20, 2012, the Prothena Business separated from Elan. *Liquidity and Business Risks* As of June 30, 2013, the Company had an accumulated deficit of $20.6 million and cash and cash equivalents of $112.5 million. Based on the Company’s current business plans, management believes that the Company’s cash and cash equivalents at June 30, 2013 will be sufficient to meet the Company’s obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on development programs significantly above current long-term plans or enters into potential licenses and or other acquisitions of complementary technologies, products or companies, the Company will need additional capital. The Company expects to continue to finance future cash needs that exceed its operating activities primarily through its current cash and cash equivalents, and to the extent necessary, through proceeds from public or private equity or debt financings, loans and collaborative agreements with corporate partners or other arrangements. The Company is subject to a number of risks, including but not limited to: the uncertainty of the Company’s research and development (“R&D”) efforts resulting in future successful commercial products; obtaining regulatory approval for new products; its ability to successfully commercialize its product candidates, if approved; significant competition from larger organizations; reliance on the proprietary technology of others; dependence on key personnel; uncertain patent protection; dependence on corporate partners and collaborators; and possible restrictions on reimbursement from governmental agencies and healthcare organizations, as well as other changes in the health care industry. *Use of Estimates* The preparation of the condensed consolidated financial statements in conformity with Generally Accepted Accounting Principles in the United States (“GAAP”) requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.

1. Organization

Description of Business

Prothena Corporation plc (“Prothena,” the “Company,” “we,” “our” or “us”), a public limited company incorporated in Ireland, is a clinical stage biotechnology company focused on the discovery and development of novel antibodies for the potential treatment of a broad range of diseases that involve protein misfolding or cell adhesion. The Company is focused on the discovery and development of potential therapeutic monoclonal antibodies directed specifically to disease causing proteins. These potential therapies have a broad range of indications including AL and AA forms of amyloidosis (NEOD001), Parkinson’s disease and related synucleinopathies (PRX002) and autoimmune diseases and metastatic cancers (PRX003). The Company has initiated a Phase 1 clinical trial for NEOD001 with the first patient dosing in April 2013. The Phase 1 clinical trial of NEOD001 will evaluate safety and tolerability in AL Amyloidosis patients. The Company’s strategy is to identify antibody candidates for clinical development by applying its extensive expertise in generating novel therapeutic antibodies and working with collaborators having expertise in specific animal models of disease.

Prothena’s business consists of a substantial portion of Elan Corporation plc’s (“Elan”) former drug discovery business platform, including Neotope Biosciences Limited (and its wholly-owned subsidiary Prothena Biosciences Inc) and Onclave Therapeutics Limited, each former wholly-owned subsidiaries of Elan (which for the period prior to separation and distribution are referred to herein as the “Prothena Business”). Effective December 20, 2012, the Prothena Business separated from Elan.

Liquidity and Business Risks

As of June 30, 2013, the Company had an accumulated deficit of $20.6 million and cash and cash equivalents of $112.5 million. Based on the Company’s current business plans, management believes that the Company’s cash and cash equivalents at June 30, 2013 will be sufficient to meet the Company’s obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on development programs significantly above current long-term plans or enters into potential licenses and or other acquisitions of complementary technologies, products or companies, the Company will need additional capital. The Company expects to continue to finance future cash needs that exceed its operating activities primarily through its current cash and cash equivalents, and to the extent necessary, through proceeds from public or private equity or debt financings, loans and collaborative agreements with corporate partners or other arrangements.

The Company is subject to a number of risks, including but not limited to: the uncertainty of the Company’s research and development (“R&D”) efforts resulting in future successful commercial products; obtaining regulatory approval for new products; its ability to successfully commercialize its product candidates, if approved; significant competition from larger organizations; reliance on the proprietary technology of others; dependence on key personnel; uncertain patent protection; dependence on corporate partners and collaborators; and possible restrictions on reimbursement from governmental agencies and healthcare organizations, as well as other changes in the health care industry.

Use of Estimates

The preparation of the condensed consolidated financial statements in conformity with Generally Accepted Accounting Principles in the United States (“GAAP”) requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses. Because of the uncertainties inherent in such estimates, actual results may differ materially from these estimates.