Obstructive sleep apnea hypoventilation syndrome (OSAHS) is an important public health problem. However, major gaps exist in our knowledge about the clinical features of this disorder in the pediatric age group. The purpose of this study was to examine clinical features of OSAHS diagnosed by polysomnography in otherwise healthy children. In this cross-sectional study, 326 children without underlying medical conditions (5.8+/-3.0 years, range 1-12 years; 56% male) were recruited from patients referred by primary care and otorhinolaryngology physicians for evaluation of snoring and difficulty breathing. Ethnic group distribution was African-American (38%), Caucasian (30%), and Hispanic (31%). Complaints of daytime tiredness or sleepiness were reported in 29% of the children. All children underwent overnight polysomnography (N = 330 studies). OSAHS was diagnosed in 59% of the children, based on polysomnographic criteria. The remaining children had either primary snoring (25%); no snoring (10%), or upper airway resistance syndrome (6%). Neither male gender nor obesity increased the likelihood for the diagnosis of OSAHS. However, the incidence of obesity in the study population (28%) was more than twice that of the general pediatric population. African-American children had a greater likelihood for OSAHS diagnosis compared to Hispanic or Caucasian children. Daytime complaints of sleepiness or tiredness were not more common in children diagnosed with OSAHS than in the children without OSAHS. As expected, tonsillar hypertrophy increased the likelihood of OSAHS diagnosis. In summary, many of the clinical features of childhood OSAHS are in marked contrast to those in adults.