• Night-float systems have recently been proposed as a way to reduce resident stress resulting from irregular sleep patterns. We prospectively evaluated the effects of a night-float system in which designated residents relieved on-call senior residents and interns of routine admissions of patients in medically stable condition during the late-night period (11 pm to 7 am). Senior residents (3.7 vs 2.4 hours) and interns (3.7 vs 3.2 hours) reported sleeping more under the night-float system than under the traditional system. The night-float system did not affect residents' overall ratings of call nights. Educators who reviewed medical records agreed with residents' decisions about patients' appropriateness for admission using the night-float system in 95 (81 %) of 117 cases. When educators disagreed with residents, the most common reasons were the patient's potential educational value or medical instability. The night-float system did not affect interns' ratings of the educational value of late-night admissions or parents' ratings of satisfaction with medical care. We conclude that the night-float system can increase resident sleep with little cost to parent satisfaction, but standards for selective use may be needed to avoid compromising patient care and resident education.