This study examined more than 11,000 medication prescribing errors in order to understand the most common types and offer potential prevention strategies. Staff pharmacists detected, recorded, and evaluated each prescribing error and categorized them for further analysis. Findings include a marked increase in the number of errors from 1987 to 1995, including increases in the rate of errors per order per admission. The most common type of error involved dosing. The authors conclude by suggesting a number of strategies, such as the use of information technology and the availability of pharmacists, to counter the perceived growth of medication prescribing errors in the hospital setting.