Accuracy of dispensing was studied in the outpatient pharmacy setting, and error rates were compared with workload. All prescriptions filled in an outpatient pharmacy over 12 weekdays were audited to determine the rate of dispensing errors. In this pharmacy, pharmacists filled prescriptions and technicians delivered the medications to the patients. Before the medication reached the patient, the auditors recorded any dispensing errors and determined whether they were potentially serious. Of the 9846 prescriptions filled, 1229 (12.5%) contained a total of 1371 errors. Of these errors, 155 (1.6%) were potentially serious. Statistical analysis of the data revealed differences between error rates and (1) the total number of prescriptions dispensed per hour and (2) the number of prescriptions filled per pharmacist hour. However, no correlation existed between the number of prescriptions dispensed per hour and the total number of errors made. No significant correlation was found between the rate of potentially serious errors and increasing work volume, suggesting that important factors in error avoidance are continuous quality improvement mechanisms and minimal interruption of dispensing. No association was found between work volume and the number of dispensing errors or potentially serious errors. Error rates were consistent with published estimates.