This study aimed to determine the prevalence of clinical depression as defined by ICD-10 criteria in all patients with obstructive sleep apnea (OSA) referred to a sleep center. Prospective general and sleep evaluations were conducted in 447 consecutive patients referred to our sleep center during the first quarter of 2008. Inclusion criteria were Apnea Hypopnea Index (AHI) >9, completion of the Beck Depression Inventory (BDI-II) with a score >= 14 and World Health Organization WHO-5 Well-Being Index (WHO-5)9. Out of these, 85 met the combined screening criterion BDI II >= 14 and WHO-5 <= 13. Eighty-one patients underwent a psychiatric examination by psychiatric sleep specialists. In 21.5 % of the sample, clinical depression was diagnosed. Other complaints existed in 12 % (n = 10); 7 % (n = 6) of patients had a different psychiatric diagnosis. The prevalence of clinical depression according to ICD-10 criteria in a selected clinical sample (referred to the sleep center) was 21.5 %. Mood scales tend to overestimate complaints as compared to psychiatric consultation. Interdisciplinary cooperation is recommended for both OSA patients with symptoms of depression and depressed patients with treatment resistance.