Although breastmilk is the best food source for the first six months of life, breastfeeding rates at three and six months of age in New Brunswick are quite low. To determine action priorities to increase the duration of breastfeeding, we tried to identify its most important determining factors. Data were obtained from the 431 breastfeeding mothers in a representative sample of 777 infants born after a normal pregnancy. The mother's knowledge about breastfeeding is the most valuable factor that explains breastfeeding duration, followed by the compatibility of the mother's employment with breastfeeding. Interventions directed at improving either of these two factors should be encouraged particularly among mothers of lower socioeconomic status who breastfeed for shorter periods of time.