This study evaluated the strength of the independent effects of social position (expressed by educational level) and number of childbirths on body mass index (BMI) variation of Polish adult females. The material comprised 2045 pre-menopausal women aged 35–50, who were healthy and occupationally active inhabitants of the city of Wrocław, Lower Silesia, Poland. Two-way analysis of variance (ANOVA) revealed that both educational level (F=34·7; p=0·0001) and parity (F=5·6; p=0·001) exerted independent significant effects on BMI. The mean BMI of women who had attended basic vocational or trade school at the very most (27·0 kg/m2) was greater than that of women who had completed secondary school education or had graduated from university (25·3 kg/m2). However, it is worthy of note that there were no social differences in BMI values between childless women. Nevertheless, an increasing number of childbirths was essentially related to increasing female BMI in each social group, and this tendency was most marked among women of lower social position. Regardless of educational level, the highest prevalence of obesity (BMI exceeding 30 kg/m2) was found among females with at least three children (15·6% and 26·4% of women from higher or lower social groups, respectively).