The aim of the present investigation was to determine the prevalence of the metabolic syndrome among 103,68 of the adults (4,397 men and 5,971 women) aged 20 years and over, participating in the Tehran Lipid and Glucose Study. The metabolic syndrome was defined by the presence of three or more of the following components: abdominal obesity, hypertriglyceridemia, low HDL-C, high blood pressure, and high fasting glucose. The unadjusted prevalence of metabolic syndrome in the study population was 30.1% (CI 95%: 29.2-31.0) and age-standardized prevalence was 33.7% (CI 95%: 32.8-34.6). The prevalence increased with age in both sexes. The metabolic syndrome was more commonly seen in women than in men (42% vs. 24%, P<0.001). Low HDL-C was the most common metabolic abnormality in both sexes. Except for high FPG, all abnormalities were more common in women than in men (P<0.001). Most of those with metabolic syndrome had three components of the syndrome (58%), 33% had four, and 9% had five components. This report on the metabolic syndrome from Iran shows a high prevalence of this disorder. Efforts on promoting healthy diets, physical activity, and blood pressure control must be undertaken.