Objectives: We aimed to 1) investigate the prevalence of MS in apparently healthy, non-hypertensive non-diabetic individuals living in Jeddah using the IDF and the NCEP-ATP III criteria to test for agreement in classification, and to determine the characteristics of subjects identified by either definition, and 2) examine the significance of family medical history and life style habits. Methods: 557 apparently healthy individuals aged 18 - 50 y were randomly approached in Jeddah health centres. 412 agreed to participate, while 55 were excluded because they were found to be frankly hypertensive and/or diabetic. Finally, 357 apparently healthy subjects with no hypertension or diabetes were fully studied. Anthropometric and demographic information were collected. Insulin, glucose, and lipid profile were obtained in fasting blood samples. Individuals were identified using the two definitions of metabolic syndrome, and their characteristics were compared statistically to the rest of the population. Results: Of the 233 subjects fulfilling the inclusion criteria, 44 and 39 (18.9% and 16.7%) were identified as having MS by the IDF or ATPIII definitions, respectively. The most common characteristic was central obesity using the IDF definition, and low HDL-cholesterol using the NCEP-ATP III definition. As expected from our exclusion criteria, the least common feature was high blood pressure in both cases. There was no significant difference between subgroups with and without MS with regard to smoking, exercise, and family history of disease. Regression analysis indicated the strongest predictors of MS were: blood glucose, LDL-C/HDL-C ratio and plasma insulin using the NCEP-ATPIII definition, and blood glucose, Waist /Hip ratio and plasma atherogenic index (PAI) using the IDF definition. Conclusions: In the absence of local cut-off thresholds for waist circumference, subjects might escape diagnosis using the IDF definition. The use of waist/Hip ratio, LDL-C: HDL-C, PAI and circulating insulin help with the diagnosis.