Subsequent pregnancies in mothers of a birth cohort from Pelotas, Southern Brazil, were studied in relation to maternal and socio-economic factors. Within about 3 1/2 years of the cohort child's birth, 39% of mothers had experienced at least one further pregnancy. This proportion decreased with increasing maternal age, years of schooling and family income. A U-shaped trend was observed with respect to parity. Mothers who had delivered the cohort child by caesarean section were also less likely to have another pregnancy within that time. Logistic regression analysis showed that each of these factors remained significantly associated with further pregnancies after controlling for the remaining variables. Analysis of the first subsequent pregnancy showed that a high proportion of mothers had not wanted the pregnancy. Unwanted pregnancies were also significantly associated with older women, low educational status, higher parity and low family income.