The aim of this study was to estimate the prevalence of metabolic syndrome in Saudi adult women aged 18 years and above using the criteria of International Diabetes Federation (IDF) and modified National Cholesterol Education Program Adult Treatment Panel III (mNCEPATPIII). A cross-sectional survey was performed involving a group of 2577 non-pregnant Saudi women subjects aged 18-59 years residing in a military city in northern Saudi Arabia recruited from a primary care setting. Anthropometric data, together with a brief medical history, were obtained at initial contact, and laboratory investigations were performed on the following day after fasting for 12 h. Data on all variables required to define the metabolic syndrome according to IDF and mNCEP-ATPIII criteria were available for only 1922 subjects who attended the laboratory for investigations (response rate of 74.6%). Non-respondents were excluded from data analysis. Prevalence rates were estimated according to both definitions. Age-adjusted prevalence of metabolic syndrome was found to be 16.1% and 13.6% by IDF and mNCEP-ATPIII definitions, respectively. Abdominal obesity was the most common component in the study population (44.1% by mNCEP-ATPIII and 67.9% by IDF cut-off points). It was followed by low serum high-density lipoprotein cholesterol (36.0%). About two-thirds of the subjects (66.4% by mNCEP-ATPIII and 67.9% by IDF definitions) exhibited at least one criterion for metabolic syndrome by both definitions. Mean values and prevalence of individual components of the syndrome showed a steady rise with increase in age, general and abdominal obesity, and the presence of diabetes. Since the cut-off values for waist circumference by IDF definition were lower, prevalence rates by this definition were higher than those defined by mNCEP-ATPIII. High prevalence rates in this young sample predict a sharp rise in the prevalence rates of this syndrome among Saudi women over the next few years.