INTRODUCTION: Obesity is a well known risk factor for obstructive sleep apnea (OSA). Medical therapy is not effective for morbid obesity. Bariatric surgery is therefore a reasonable option for weight reduction for patients with clinically severe obesity. PATIENTS AND METHODS: 283 obese patients were operated on from 1999 until 2005 in our Institution and they were examined with a history, physical examination and the Epworth Sleepiness Scale (ESS). Obese patients with a ESS score ≥ than 10 were evaluated with a Polysomnography (PSG). RESULT: 61 patients (21.5%) resulted with a ESS ≥ than 10. An obstructive sleep apnoea syndrome was identified in 52 patients (85.2%).These patients were treated by continuous positive airway pressure (CPAP) for 3 months before the surgical treatment. After 1 year follow-up (100% of patients) we observed a reduction in OSAS patients: ESS <10 in 77.5% and PSG negative in 80.3%. CONCLUSION: This study considered the value of ESS to select obese patients with a high risk of OSA. We did not observe any association between grade of obesity and risk of OSA. Bariatric surgery reduced the prevalence of OSA already after 1 year of follow-up and the preoperative treatment of OSA (3 months CPAP) reduced the post-operative morbidity.