With growing adoption of information technology systems designed to improve the safety and quality of care, this study prospectively evaluated the incidence and epidemiology of adverse drug events (ADEs) in a computerized inpatient setting. After implementation of electronic resources at a Veterans Administration hospital (eg, electronic medical records [EMRs], computerized provider order entry [CPOE], integrated checking of allergies and drug-drug interactions, and bar coding), pharmacists identified and categorized nearly 500 ADEs over a five-month period. Results suggested that 25% of hospitalizations were associated with at least one ADE, accounting for an event rate of 52 ADEs per 100 admissions. The majority of errors that resulted in an ADE occurred in the medication ordering phase. The authors conclude that while there is a capacity to safely administer drugs using computers, more appropriate decision support at high-risk steps would improve current systems.