The extent of son preference and its effect on desire for additional children and contraceptive use is examined for rural Bangladesh. Our results show that there is strong son preference, expressed through contraceptive behaviour and desire for additional children, on the part of rural Bangladeshi women. In deciding whether or not to have an additional birth or the use contraception, sex composition of children and number of sons are the most important determinants. Most couples are guided in their desire for additional children by an ideal sex composition which is commonly found to comprise two to three sons and one daughter. Bangladeshi women want to have children of both sexes but their preference for sons is much stronger and the number much larger compared to those for daughters. It can be argued from our findings that if the desired number of sons and daughters have already been born, women will be more likely to use contraception and less likely to want additional children.