 The specific aims are to determine the incidence of medication errors related to antimicrobial prophylaxis for cardiovascular surgery, joint replacement surgery, and hysterectomies across a heterogeneous sample of hospitals; identify organizational and practitioner factors associated with error rates, and evaluate the effectiveness of a multifaceted intervention in reducing prophylaxis error rates compared to written feedback alone in a sample of 44 hospitals enrolled in the study using a rigorous group-randomized design. 