Phototherapy has been shown to be an effective therapy for severe neonatal jaundice. However, because of its seemingly innocuous effect on normal babies, this therapeutic modality has been widely used to prevent jaundice in circumstances where it may be neither necessary nor beneficial. The present report summarizes results which indicate that phototherapy is endowed with DNA-modifying properties and has therefore the potential for inducing genetic and carcinogenic effects. These disconcerting findings concerning the long-term hazardous consequences of an accepted therapeutic procedure require that the unique physiologic and pharmacologic characteristics of the newborn populations be recognized when assessing the risks and benefits of phototherapy.