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The association among breastfeeding variables, maternal age, and resumption of menses postpartum was examined in a longitudinal study in Indonesia. Breastfeeding information was elicited by monthly recall. Three breastfeeding variables, 1) number of bouts during the day, 2) number of bouts during the night, and 3) number of minutes per nursing bout were derived as means over all months of breastfeeding up to return to menses or censoring which ever came first. The proportional hazards model, which has not previously been used to examine the biobehavioral determinants of postpartum amenorrhea, was applied to postpartum amenorrheic survival data to simultaneously adjust for censoring and relationships among variables. Three age categories were also investigated, ages 15-24, 25-34, and 35—49. Age and the three breastfeeding variables were all significantly related to return to menses. Low intensity breastfeeding with 3 or fewer bouts at night, 6 or fewer bouts during the day, and 6 minutes or less of nursing per bout, and younger age, all increase the risk of early postpartum resumption of fecundity in these Indonesian mothers.