OBJECTIVE: The aim of this study was to evaluate the motivational determinants of the continuation of breast-feeding until 3 months postpartum. METHODS: A prospective cohort study using the Integrated Change Model in 341 women in 5 child health care centers. RESULTS: At birth, 73% of the mothers started with breast-feeding and 39% of them continued at least 3 months postpartum. Mothers who continued for 3 months differed in almost all the motivational determinants from mothers who discontinued. In the multiple logistic regression analysis, social support for formula feeding from significant others and situational self-efficacy for breast-feeding made a significant independent contribution to the continuation of breast-feeding. Among the predisposing determinants, the strongest positive predictor of continuation was the intention to return to work at 1 month postpartum. CONCLUSION: The Integrated Change Model is valid to explain and predict the continuation of breast-feeding. Hence, the results may be used to tailor future interventions aimed at promoting breast-feeding. In the discussion, we use the results to target interventions.