This paper discusses polygynous marriages in rural Bangladesh, using marital status and birth registration data from the Demographic Surveillance System of the International Centre for Diarrhoeal Disease Research, for the period 1975–79. Of all the marriages recorded during this period about 5% were polygynous. To identify the women polygynously married, 1974 census data of the DSS area were used. The difference in age at marriage between the polygynous groom and his subsequent wife was 15 years on average. The socioeconomic indicators studied were education, occupation and area of dwelling space. In general, these indicators differentially influence polygynous marriage. The fertility differentials between women in monogamous marriages were significantly higher than between the women in polygynous unions.