To determine the appropriateness of use of omeprazole, all outpatient prescriptions over one year from a single county hospital pharmacy were analyzed. Appropriateness of omeprazole use was assessed by literature review and expert opinion. Two hundred twenty-one prescriptions were evaluated; 112 (56%) were inappropriate. Women received more inappropriate prescriptions (61% vs 44%, p = 0.01) and received endoscopy less frequently (52% vs 71%, p < 0.02) than did men. When age, gender, and prescribing clinic were examined as predictors of inappropriate use, only gender was significant (OR = 2.01, 95% CI = 1.52-2.66). This study, from a single institution, showed a high rate of inappropriate omeprazole use.