This study compares weight change in lactating women with an 18-month interpregnancy interval with woman who also breastfed but did not have an immediate subsequent pregnancy. Cases were women who breastfed an index infant for 6 months and subsequently became pregnant within 18 months (cases ฯญ 25), and the controls also breastfed an index infant for 6 months but had no ensuing pregnancy (controls ฯญ 20) within 18 months. The pattern of postpartum weight retention following the initial pregnancy was not statistically different in cases compared to the controls. However, following their ensuing subsequent pregnancy, cases were 1.3 kg heavier than their average weight after their baseline pregnancy (P ฯญ 0.02). The best predictor of this greater weight was their weight change during the interpregnancy interval (P ฯญ 0.03). Total weight gain during the gestational period of the subsequent pregnancy was not associated with the greater weight following the subsequent pregnancy. Likewise, estimates of the amount of energy as calories or physical activity levels were not significant predictors of this greater weight following the subsequent pregnancy. These findings suggest that monitoring of postpartum weight, even in breastfeeding women, is essential. These findings indicate that breastfeeding women begin the next postpartum interval weighing more than the amount observed in the initial postpartum period.