The obstructive sleep apnea syndrome (OSAS) is characterized by collapse of the upper airway during sleep, recurring apneas, intermittent hypoxemia and daytime somnolence. OSAS is often associated with obesity, and its prevalence is expected to rise due to the obesity epidemics worldwide. OSAS is associated with increased cardiovascular risk which appears to be normalized by treatment with nasal continuous positive airway pressure (nCPAP) during sleep, suggesting an independent role of OSAS in accelerating atherosclerosis. Insulin resistance (IR) and the metabolic syndrome (MetS) are often found in OSAS patients, but the relative role played by OSAS and obesity is still unclear. Both OSAS and MetS may exert negative synergistic effects on the cardiovascular system through multiple mechanisms (hypoxemia, sleep disruption, activation of the sympathetic nervous system, inflammatory activation). Besides nCPAP treatment, pharmacologic interventions to treat obesity and the MetS could improve cardiovascular prevention in OSAS.