From 1985 through 1995, 348 infants aged 3 wk-3 mo were referred to the Stanford Sleep Clinic for "apparent life-threatening events" (ALTE). A small group of 48 infants with no history of sleep-disordered breathing (SDB) was also recruited and used as controls (they comprised group C). We conducted a systematic investigation of relatives (parents, siblings, and grandparents) of the infants, including a clinical evaluation, craniofacial investigation, and the completion of an extensive (189-question) validated sleep/wake questionnaire. All data were calculated before the subdivision of ALTE infants into two groups. The subdivision was based on a blind scoring of the infants' polygraphic recordings; 42.5% of the infants were negative for SDB (Group A), whereas 57.5% of the infants were positive for SDB (Group B). Groups A and C were not significantly different from each other. Forty-three percent of the relatives of Group B infants had been treated for SDB (with nasal CPAP, surgical or dental appliance treatments) compared with 7.1% of Group A relatives. Clinical investigation indicated a significantly higher presence of small upper airways in the families of infants with SDB. About twice as many relatives reported the presence of asthma in Group B compared with Group A. Naso-oro-maxillomandibular anatomic traits that may lead to small upper airways in parents may be risk factors for abnormal breathing during sleep in their infants.