Obesity is an undesirable outcome of changing of lifestyle and behaviours. It is also reversible predisposing factor for the development of several debilitating diseases. This study was aimed to determine the prevalence rate of obesity, overweight, central obesity and their associated factors in the north of Iran. We conducted a population-based cross-sectional study with a sample of 1800 women and 1800 men with respective mean ages of 37.5 +/- 13.0 and 38.5 +/- 14.2 years of urban population aged 20-70 years living in the north of Iran. The demographic and lifestyle data, in particular, age, gender, marital status, marriage age, family history of obesity, educational level, occupation, occupational and leisure time physical activity, duration of exercise per week, parity and the number of children were collected with a designed questionnaire. Diagnosis of obesity and central obesity were confirmed by the WHO standard recommended method by determining of body mass index (BMI) and waist circumference (WC). Logistic regression model was used to estimate the adjusted odds ratio (OR) and its 95% confidence interval. Over half of the study subjects were at educational levels of high school or higher; 79.4% of population was married and 35.3% had a family history of parental obesity. The majority of subjects in particular women had none or low levels of physical activity. The overall prevalence rates of obesity and overweight were 18.8% and 34.8% respectively. The overall prevalence rate of central obesity was 28.3%. The rate of obesity in women was higher than men (P < 0.0001). In both genders, particularly in the women, the rate of obesity was raised by increasing age. There was an inverse relation between the risk of obesity and marriage age, the high level of education (OR = 0.19, P < 0.0001), severe occupational activity (OR = 0.44, P < 0.0001), the level of exercise (in subjects with 3-4 h exercise per week, OR = 0.58, P < 0.001) and leisure time activity. Marriage, history of parental obesity and parity > or =5 were associated with increased risk of obesity (OR = 2.2, P < 0.001 and OR = 2.43, P < 0.0001 and OR = 3.73, P < 0.0001 respectively). The results of this study indicate an increased rate of obesity and overweigh in the north population of Iran. With respect to these findings, low level of activity and education, parity, family history of obesity, marriage at earlier age and ageing are responsible for both obesity and central obesity in the north of Iran. Therefore, a community-based multiple strategies are required to combat with increasing rate of obesity and its subsequent complications such as diabetes, coronary artery disease, hypertension and osteoarthritis.