Kernicterus is a preventable life-long neurologic syndrome caused by severe and untreated hyperbilirubinemia during the neonatal period. High levels of bilirubin are toxic to the developing newborn. In full-term infants, hyperbilirubinemia symptoms include severe jaundice, lethargy, and poorfeeding. Features of kernicterus may include choreoathetoid cerebral palsy, mental retardation, sensorineural hearing loss, and gaze paresis. Kernicterus is not a reportable condition in the United States, and its prevalence is unknown; however, a pilot registry at a Pennsylvania hospital documented 90 cases in 21 states from 1984 to June 2001 (L. Johnson, Pennsylvania Hospital, Philadelphia, personal communication, 2001). This report summarizes case histories of four full-term, healthy infants who developed kernicterus and underscores that to prevent kernicterus, newborns must be screened and promptly treated for hyperbilirubinemia.