The study examined the relationship between marital status and the body mass index (BMI) and the prevalence of overweight and obesity in the Polish population. The sample included 2,266 men and 4,122 women, 25-60 years of age, who were occupationally active inhabitants of Wroclaw, in southwestern Poland. Marital status was defined by two categories: never married and presently married, and two groups in each category were established on the basis of educational level: well-educated (12 or more years in school) and poorly educated (less than 12 years in school). The subjects were also divided into four age groups: 25-30, 31-40, 41-50, and 51-60 years. Height and weight were measured and the BMI was calculated. Three categories of the BMI were established: normal, BMI < 25.0 kg/m(2), overweight, BMI > or = 25 < 30 kg/m(2), and obese, BMI > or = 30 kg/m(2). In each age and educational group, married individuals had a higher BMI than those who were never married. With the exception of well-educated males 51-60 years, differences in the BMI between married and never married individuals increased with age. In general, married men and women were more likely to be overweight and obese than never married individuals. The results indicated a significant association (P < 0.001) between marital status and the BMI in both sexes. After age, marital status was the most important predictor of overweight/obesity among men (P < 0.001), whereas educational level did not have a significant role. Among women, age, marital status, and education were significantly (P < 0.001) related to the BMI.