To define the patterns of referral of adult patients with obstructive sleep apnea syndrome (OSAS) for diagnostic sleep testing, we studied 97 consecutive patients with OSAS (Apnea/Hypopnea Index >/= 20) referred to the Center for Sleep and Ventilatory Disorders, an American Sleep Disorders Association-accredited university sleep center. Chart review and semi-structured patient telephone interview quantified the time between the onset of any major feature of OSAS and referral to the sleep center, as well as the time between the first OSAS complaint to a health care provider and referral to the center. The average time elapsed between first recognition by the patient of a major feature of OSAS to sleep center referral was 87.5 months (range, 1 to 480 months). Only 4% of referrals were made as a result of the clinician eliciting a history of sleep-related complaints. Once OSAS-related features were apparent to the clinician, the average time to referral for diagnostic testing was 7.9 months (range, 0 to 128 months). These data suggest that both a lack of reporting of symptoms by OSAS patients and a lack of obtaining appropriate sleep history by health care providers contribute to a significant delay in diagnosis of OSA.