The increased frequency of early discharge of newborns has led to questions of its safety. Most studies have looked at mortality and rehospitalization, not all missed diagnoses. The purpose of this study was to determine diagnoses in newborn infants that would have been missed if the infant had been discharged in <24 h. The design was a cohort study at Rabin Medical Center-Beilinson Campus (average monthly deliveries 1996 [250], 1997 [500]), a university-affiliated community hospital with all in-born term (> or = 37 weeks) infants born September through November 1996 and June 1997. The main outcome measures were medical diagnoses (except trivial physical descriptions) noted at discharge (generally at > or =48 h) exam, not noted on admission exam (<24 h). The results showed that 54 infants (5.1%) had diagnoses that were not detected before the infant was 24 h of age. The leading diagnosis was hyperbilirubinemia. Other potentially missed diagnoses included congenital heart disease (n = 10), morbidity of birth trauma (n = 9), metabolic disturbances (n = 2), hip dislocation (n = 1), suspected sepsis (n = 2), excessive weight loss (n = 2), polycythemia (n = 2), inguinal hernia (n = 1), and abducens paresis (n = 1). It is concluded that diagnoses can be missed by discharging infants in 24 h or less. These diagnoses have the potential for adverse sequela. Even if early discharge is felt to be cost effective, parents should be counseled that it is not risk free. Better mechanisms should be put in place for assuring the safety of such infants.