This paper examines the biosocial basis of premarital sexual and reproductive behaviour among women in Sudan. It applies Udry's biosocial perspective, which attempts to reconcile the biological and sociological models of premarital sexual and reproductive behaviour. World Fertility Survey (WFS) data were used to study premarital first motherhood. Early puberty was found to be paramount in determining childbearing in a separate biological model, but also in a biosocial model constructed to take account of social controls. This finding suggests that social controls do not influence the biological predisposition to premarital sexual behaviour. However, given the limitations of the WFS data, conclusive evidence must await a more appropriately designed study of reproductive behaviour in Sudan.