The association of obstructive sleep apnea (OSA) syndrome with obesity, hypertension and cardiovascular disease has highlighted the broad public health importance of this condition. OSA affects at least 9% to 15% of middle-aged adults. Both epidemiological and sleep clinic-based studies indicate that OSA is more common in men than in women. However, the ratio of men to women with OSA in clinical studies appears to be considerably higher than in the community: up to 8:1 versus 2 to 3:1. Cross sectional studies on OSA prevalence showed effects of age, independently from the unfortunate propensity for a rising body mass index (BMI) with age: an approximate doubling of apnea-hypopnea index (AHI) every 10 years has been reported. A recent prospective study with 4-year follow-up showed that a 10% weight gain predicted a 32% increase in AHI, whereas a 10% loss in weight predicted a 26% decrease in AHI. Another 5-year prospective study found that longitudinal change in AHI varies nonuniformly with age, sex and weight: older heavier may experience the highest rate of AHI increase over time and, thus, may benefit most from prospective monitoring.