The aim of this study was to study the effect of overweight and obesity on glucose intolerance and dyslipidemia in Saudi Arabia. A cross-sectional national epidemiological randomized household survey of 2059 Saudi subjects, aged 30-64 years was carried out. The sample was representative and was in accordance with the national population distribution with respect to age, gender, regional and residency, urban Versus rural population distribution. The subjects height and weight for the calculation of body mass index (BMI) was measured. Blood samples were drawn and assayed for glucose, total cholesterol, triglyceride and high density lipoprotein (HDL). Low density lipoprotein (LDL) was calculated. The oral glucose tolerance test was carried out for subjects with borderline random glucose concentration and the overall prevalence of diabetes mellitus was calculated. A high prevalence of obesity among the Saudi population was observed and mean serum glucose concentration was significantly higher among overweight and obese groups. The prevalence of diabetes mellitus was significantly higher among obese groups. The mean serum triglyceride concentration was only significantly higher among male obese groups. There was no significant difference in the mean of serum total cholesterol concentration between control and obese groups. Mean serum HDL concentration was lower among the obese group, however, the difference was not significant. There was no significant difference in the prevalence of hypercholesterolemia between control and obese groups. Prevalence of hypertriglyceridemia was higher among obese groups and was significantly higher among male subjects across all BMI groups. Prevalence of hypo HDL cholesterolemia exceeded 50% bf the study population. Obesity, glucose intolerance, hypertriglyceridemia, hypo HDL cholesterolemia and features of insulin resistance syndrome (IRS) are widely prevalent among the Saudi population over the age of 40 years. IRS is probable a significant contributor to the pathologic process of cardiovascular (CVD) disease among the Saudi population, especially in view of the low prevalence of hypercholesterolemia. (C) 1997 Elsevier Science ireland Ltd.