This study examined the incidence of prescribing errors that occurred on-call, post-call, and off-call for a group of residents at a single teaching hospital. Through a retrospective chart review, investigators discovered that orders written either on-call or post-call were associated with a greater error rate than those written on an off-call day. Results also suggested increased error rates with medication orders when written by less experienced residents and for patients on general medical/surgical services. The authors conclude that additional research to understand the contributing factors will provide a strategy for necessary intervention.