From 1974 to 1988, 4 cases of neonatal idiopathic prolonged penile erection were recorded, for an incidence of 0.15 per thousand or 1 case for 6,673 male newborns. Our first patient was case 7 described in the literature and the first observed in 1 of nonidentical twins. Followup for 2 to 8 years revealed no urogenital problems but a longer period (at least until puberty) is needed. Clinical and etiological aspects of this entity are discussed. Many of the etiological factors cited as possible causes of prolonged erection at this patient age represent only predisposing conditions for the occurrence of penile erection. Because of the spontaneous disappearance of prolonged penile erection, observation rather than surgical or medical management is advocated for the newborn. Only in selected patients should the limit of expectation, and the best time for and type of surgical intervention be established.