Objective: To determine opioid-prescribing patterns and rate of three types of errors, discrepancies, and variation from ideal practice.Design: Retrospective review of opioid prescriptions processed at an outpatient pharmacy.Setting: Tertiary institutional medical center.Patients: We examined 510 consecutive opioid medication prescriptions for adult patients processed at an institutional outpatient pharmacy in June 2016 for patient, provider, and prescription characteristics.Main Outcome Measure(s): We analyzed prescriptions for deviation from best practice guidelines, lack of two patient identifiers, and noncompliance with Drug Enforcement Agency (DEA) rules.Results: Mean patient age (standard deviation) was 47.5 years (17.4). The most commonly prescribed opioid was oxycodone (71 percent), usually not combined with acetaminophen. Practitioners prescribed tablet formulation to 92 percent of the sample, averaging 57 (47) pills. We identified at least one error on 42 percent of prescriptions. Among all prescriptions, 9 percent deviated from best practice guidelines, 21 percent failed to include two patient identifiers and 41 percent were noncompliant with DEA rules. Errors occurred in 89 percent of handwritten prescriptions, 0 percent of electronic health record (EHR) computer-generated prescriptions, and 12 percent of non-EHR computer-generated prescriptions. Interrater reliability by κ was 0.993.Conclusions: Inconsistencies in opioid prescribing remain common. Handwritten prescriptions continue to demonstrate higher associations of errors, discrepancies, and variation from ideal practice and government regulations. All computer-generated prescriptions adhered to best practice guidelines and contained two patient identifiers, and all EHR prescriptions were fully compliant with DEA rules.