Introduction The prevalence of Obstructive Sleep Apnea Syndrome (OSAS) is known to be higher among obese patients. This study aims to evaluate the prevalence of OSAS in obese individuals. Materials and methods We conducted a cross-sectional study in a sample of patients referred for sleep polysomnography before bariatric surgery. The severity of OSAS was categorized by the apnea–hypopnea index (AHI) as follows: absent 30 events per hour. Baseline demographic and sleep study data were registered. Results One hundred and thirty-four (134) patients were enrolled (21 male, 113 female), with a mean age of 44.9 years (range 19 to 64 years). The body mass index (BMI) was averaged 44.5 kg/m 2 and ranged from 32.7 to 68 kg/m 2 . Eighty patients (60%) presented OSAS, with an AHI averaged 17.2 events per hour (40 mild, 14 moderate and 26 severe disease). The mean ODI was 19 desaturations per hour. We observed a significantly statistical difference between male and female patients, with men experiencing a higher prevalence of disease (100%), a more severe disease (mean AHI of 42 events per hour in male and 12 events per hour in female) and a higher ODI (41.4 in male and 14 in female). Conclusion OSAS had a prevalence of 60% in obese patients referred to a multidisciplinary obesity treatment unit. We observed that men experienced a higher prevalence and a more severe disease, as described in literature.