To assess the impact of direct supervision of resident physicians by attending physicians on quality of care in emergency departments. In 1993, compliance with process-of-care guidelines was measured for 3,667 patients cared for by residents in five emergency departments in Boston and Cambridge, Massachusetts. Those patients presented with abdominal pain, asthma/COPD, chest pain, hand laceration, head trauma, or vaginal bleeding. A follow-up survey to assess patient satisfaction and reported problems with care was completed by 1,094 randomly sampled patients. In multivariate analysis, residents directly supervised by attending physicians had significantly (p < .0001) higher adjusted mean percentage compliance with guidelines (64%) than did residents alone (55%). Better compliance was also associated with higher level of training of the resident and greater patient urgency. There was no significant difference between supervised and unsupervised residents in either adjusted patient satisfaction or reported problems with care. Direct supervision of residents in emergency departments is significantly associated with better compliance with guidelines, regardless of level of training. However, direct supervision was not shown to influence patients' experience with care.