We present the case of a 52 year-old obese (BMI = 46.2 kg/m(2)) man with severe obstructive sleep apnea (RDI of 60). Before CPAP treatment was applied, the patient was diagnosed with complete respiratory failure and polycythemia. During effective autoCPAP treatment (after 10 days AHI was 5.5 at 10 mbar pressure) we observed normalization of arterial blood gases (PaCO(2) of borderline value). After one month's treatment with autoCPAP at home, we found normalization of blood morphology parameters and PaCO(2) had returned to normal, and the patient was properly oxygenated. The patient lost 22 kg during therapy (9 kg in hospital, and 13 kg at home) which resulted in the spirometric measurements returning to their normal value.