This study evaluates the incidence and preventability of adverse drug events (ADEs) at a tertiary care hospital. All patients on seven units were followed prospectively, and ADEs were determined by solicited reporting by nurses and pharmacists, as well as independent chart review. The rate of ADEs was 10 per 1000 patient-days, or approximately 6 per 100 admissions. Physicians were responsible for 72% of the incidents, and 56% of the ADEs were believed to be preventable. The authors found that 67% of the ADEs were identified only by chart review and not by solicited reporting. The article concludes that ADEs are not infrequent, often preventable, and usually caused by physicians.