X0304 4 2012-03-20 0 0001018399 ENTERPRISE BANCORP INC /MA/ EBTC 0001462721 Szablak Chester J JR C/O ENTERPRISE BANCORP, INC. 222 MERRIMACK STREET LOWELL MA 01852 0 1 0 0 EVP - Principal Subsidiary Common Stock 2012-03-20 4 A 0 2100 0 A 19945.7497 D Stock option (Right to buy) 16.25 2012-03-20 4 A 0 1500 0 A 2019-03-19 Common stock 1500 1500 D Includes 1.5643 shares acquired through the Issuer's Employee Stock Purchase Plan on 6/7/11 Includes 2.1807 shares acquired through the Issuer's Employee Stock Purchase Plan on 9/8/11 Includes 2.1239 shares acquired through the Issuer's Employee Stock Purchase Plan on 12/7/11 Includes 2.0189 shares acquired through the Issuer's Employee Stock Purchase Plan on 3/7/12 Option vests 25% per year on the anniversary of the grant date with the first installment vesting on 3/20/13 /s/ John P. Clancy, Jr. as attorney-in-fact for Chester J. Szablak, Jr. 2012-03-22