The distribution of symptoms, physiologic responses, and upper airway structure in members of one family with three generations of subjects with sleep apnea (SA) is reported. Questionnaire data were obtained from ten family members (ages 7 to 66 years), overnight sleep studies were performed in nine subjects, and ventilatory responses to hyperoxic hypercapnia and to eucapnic hypoxia and cephalometry were obtained in five subjects. All ten family members reported habitual snoring or nighttime snorting/gasping; five of ten family members also reported excessive daytime sleepiness. All studied subjects except for a pregnant woman had greater than ten apneas/hypopneas per hour. Ventilatory responses to hypoxia were markedly reduced in all five subjects studied (less than or equal to 0.51 L/min/SaO2); hypercapnic responses were reduced in three of five subjects (less than or equal to 0.61 L/min/mm Hg CO2). No subject was morbidly obese (body mass index less than 29 kg/m2) or demonstrated retrognathia. The posterior airway space was reduced in three subjects, and the mandibular to hyoid distance was increased in four subjects. The two subjects with the longest soft palates and the most inferiorly displaced hyoids had the most severe sleep disorder. Sleep apnea was present, albeit less profound, in the one subject with normal anatomy who had an abnormal hypoxic ventilatory response. The distribution of these physiologic and anatomic measurements in this family provides further support for a genetic basis for SA, and suggests that the disorder may occur as a result of interactions between ventilatory control abnormalities and anatomic risk factors.