Obstructive sleep apnea syndrome (OSAS) is characterized by repeated episodes of upper airway obstruction during sleep. Most subjects with OSAS are obese. Leptin, a hormone produced by adipocytes, plays a regulatory role on body weight. Increased leptin levels occur in obese patients with OSAS. Our objective was to determine the anthropometric characteristics and examine the relationship between circulating leptin levels and sleep-related breathing disorders in a group of obese patients with OSAS. Twenty-eight patients with confirmed OSAS underwent overnight polysomnography; in addition, anthropometric measurements were performed and serum leptin levels were determined. No correlation was detected between AHI and any of the examined anthropometric characteristics. The mean levels of circulating leptin (±SD) were 15.5 ng/mL (±11.9). Serum leptin levels did not correlate with AHI, even when adjusted for fat mass. Moreover, no correlations between leptin levels and sleep time with oxygen saturation <90%, or lowest level of oxygen saturation during sleep were found. Serum leptin levels correlated with BMI and abdomen circumference. Circulating leptin levels and anthropometric measures in subjects with OSAS are not related to the severity of sleep apnea, as assessed by AHI or other sleep-disorder parameters, such as sleep time with oxygen desaturation <90%% and lowest level of oxygen saturation during sleep. Pneumon 2006,19(2):124-130.