1. Duration of lactational amenorrhoea and interpreganancy interval were related to maternal body-weight in an urban low-income group population of 2250 women.
2. Breast-feeding practices were similar in all the women, none of whom had received any nutritional intervention.
3. In the study group the mean duration of lactation, lactational amenorrhoea and interpregnancy interval (months) were 20.7, 11.2 and 24.2 respectively.
4. Mean duration of lactation was significantly shorter in women whose body-weights were over 55 kg. Duration of lactational amenorrhoea increased with increasing duration of lactation (r 0.5164).
5. The duration of lactational amenorrhoea showed a progressive fall with increasing body-weight (r − 0.8139) even when duration of lactation was kept constant.
6. The mean duration of post-partum amenorrhoea in women who did not lactate remained unaltered irrespective of body-weight.
7. The findings suggest that maternal nutritional status modifies return of menstruation only in lactating women.