Obstructive Sleep Apnea (OSA) is defined by the presence of repetitive episodes of upper airways collapse during sleep, leading to nocturnal hypoxemia, sleep fragmentation and daytime sleepiness. When untreated, OSA is a risk factor for arterial hypertension , cardiovascular and cerebrovascular diseases, road accidents and a worse quality of life. The application of a continuous positive airways pressure (CPAP) represents the first line therapy in patients with moderate to severe OSA. CPAP treatment improves daytime sleepiness and oxygen saturation, reduces cardiovascular risk, ameliorates neurobehavioral performance, improves quality of life and reduces road accidents. Despite its demonstrated efficacy, CPAP effectiveness is significantly limited by poor adherence. A closer follow up could improve CPAP adherence but it would take up more work and additional costs for sleep units.