Background Rare are the studies that focus on OSAS (obstructive sleep apnoea syndrome) obese patient assessing neuropsychological, psychological and clinical aspects simultaneously. Methods One hundred and fifty-seven obese patients with OSAS were psychologically and neuropsychologically assessed by a standardized battery of validated tests in a cross-sectional study. Results Patients reported with higher frequency, compared to the normal distribution, the presence of an extrovert personality trait and depressive behaviours: 15.9% of the patients minimized symptoms and denied distress, whereas 28.0% presented psychological disorders. Compared to the normative group, patients’ results were characterized as impaired with a higher percentage in short-term verbal memory (30.6%) and in short-term visual spatial memory (20.5%). Moreover 30.6% of patients were impaired in one cognitive function, 11.5% in two, 8.9% in three, and 8.2% in four or more cognitive functions. No significant relations between psychological–neuropsychological data and clinical variables emerged. Conclusions The results of our obese patients with OSAS were significantly different from the normative data as for psychological and neuropsychological variables (extroversion, depression, short-term verbal and visual spatial memory, logical ability). Further studies are needed in order to investigate the eventual dose effect on psychological and neuropsychological variables of OSAS and obesity severity and treatment efficacy.