This study investigated the impact of hospital pharmacists in preventing medication errors. For more than 123,000 medication orders at a single university teaching institution, the overall error rate was approximately 2%. Incorrect dosage, inappropriate dosing schedules, and omission of essential information represented the most common error types. Physicians confirmed an error in more than 90% of orders questioned by pharmacists. The authors conclude that the use of hospital pharmacists to screen every medication order prevents almost 9000 errors annually.