The primary aim is to study whether a tailored behavioural medicine intervention addressing physical activity and eating habits have additional effects to continuous positive airways pressure (CPAP) in patients with moderate or severe obstructive sleep apnea syndrome (OSAS) combined with obesity. Direct everyday life consequences (see below) of OSAS are studied, as well as cognitive functions and ventilatory parameters. Long-term benefits will be examined in terms of quality of life and everyday life activity. Another aim is to study mechanisms of treatment effects, if any.