[show abstract][hide abstract] ABSTRACT: The aim of the study was to determine the prevalence of metabolic syndrome (MeS) in professional bus drivers, and its association with overtime working hours among those drivers in Urmia, Iran. In this cross sectional study the studies population was 626 professional bus drivers, aged 20-69 yr. The MeS (according to the National Cholesterol Education Program Adult Treatment Panel III), Waist circumference, Systolic blood pressure, Diastolic blood pressure, Fasting plasma glucose, Triglyceride, HDL-cholesterol, age, and working time per week. The overall prevalence of the metabolic syndrome was 32.4%. The prevalence of the MeS was higher than the general Iranian population. There was a statistically significant positive relationship between over time driving and MeS (P: 0.028). This represents an odds ratio of 1.46 (95%CI: 1.04 – 2.05). The metabolic syndrome is becoming a noteworthy health problem in bus drivers; therefore, early detection and appropriate intervention need to be established. INTRODUCTION The metabolic syndrome (MeS) is a complex association of several interrelated abnormalities that increase the risk of cardiovascular events and progression to diabetes mellitus [ 1-6]. Age-adjusted MeS prevalence among adults aged 20–70 years in the USA has been reported to be 24% in men [ 7]. Reaven et al. described the MeS or insulin resistance syndrome in 1988 [ 8]. In 1998, World Health Organization (WHO) [ 9] provided a definition of the MeS. Although there are several definitions, the most commonly used are the NCEP criteria to clinically identify patients .The National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATP III) released a definition in 2001, and proposed that the MeS can be recognized clinically by a clustering of simple clinical measures [ 10-12]. The drivers' working environment is characterized by numerous stress factors such as lack of physical activity due to overtime working in a fixed position, disruption in diet, and sleep habits caused by irregular work schedule [ 13, 14]. Ever since the 1950s, researchers have been looking at the causes of heart diseases in bus drivers. Fifty-four years ago, Morris et al., reported lower rates of coronary heart disease in bus conductors than in less occupationally active bus drivers. This seminal U.K investigation was undertaken using data from two cohorts of British workers [ 15]. Long distance professional drivers have particular life styles. They are likely to take fast foods frequently and fail to exercise regularly. The objectives of this study were to estimate the prevalence of the MeS using the NCEP-ATP III definition among professional long distance drivers as a subgroup of general population, and to determine the role of overtime working on MeS.