The authors report their 1991 survey on medical errors among internal medicine house officers at three large academic medical centers. Their survey revealed a surprisingly high rate of acknowledged serious errors, many contributing to patient deaths. House officers cited knowledge deficits, inexperience, lack of supervision, errors in judgment, overwork, and fatigue as underlying factors and largely accepted personal responsibility for their mistakes. Errors were infrequently discussed with supervising physicians, patients, or patients’ families.