X0303 4 2011-02-21 0 0001171500 PLATINUM UNDERWRITERS HOLDINGS LTD PTP 0001354076 Porter Robert S THE BELVEDERE BUILDING 69 PITTS BAY ROAD, 2ND FLOOR PEMBROKE D0 HM 08 BERMUDA 0 1 0 0 CEO - Platinum Bermuda Common Shares 2011-02-21 4 M 0 6188 0.00 A 133444 D Common Shares 2011-02-21 4 M 0 3133 0.00 A 136577 D Common Shares 2011-02-21 4 A 0 14950 0.00 A 151527 D Share units 2011-02-21 4 M 0 6188 0.00 D Common Shares 6188 0 D Share units 2011-02-21 4 M 0 3133 0.00 D Common Shares 3133 3132 D These share units represent the payment of an award granted on February 21, 2008 under the Amended and Restated Executive Incentive Plan of Platinum Underwriters Holdings, Ltd. (the "Company") for the 2008-2010 performance cycle. 1-for-1 These share units were awarded on May 30, 2007 under the 2006 Share Incentive Plan of the Company. On February 21, 2011, the remaining 50% of these share units vested and the Company issued to the reporting person one Common Share for each vested share unit. These share units were awarded on February 21, 2008 under the 2006 Share Incentive Plan. On February 21, 2011, 50% of these share units vested and the Company issued to the reporting person one Common Share for each vested share unit. On February 21, 2012, the Company will issue to the reporting person one Common Share for each of the remaining 50% of the share units awarded to the reporting person. /s/ Michael E. Lombardozzi, Attorney-in-Fact 2011-02-22