Background: Breastfeeding is the gold standard of infant feeding due to the many advantages it offers to both the child and the mother. Objective: To identity the main reasons for cessation of breastfeeding reported by mothers during the first year of life. Design: A prospective cohort study was conducted, recruiting 970 infants from a university hospital in Spain. The main maternal variables studied were maternal age, parity, educational level, work occupation, smoking habit, weeks of gestation at birth, birth weight, feeding type, and duration of breastfeeding. All participants were followed for one year to determinate the duration of breastfeeding and to gather reasons for abandoning breastfeeding. Results: At six months, the percentage of breastfeeding experienced a decline of 50%, and only 24.5% of these mothers maintained breastfeeding. Up to 15.8% of the mothers decided to give up exclusive breastfeeding by their own choice, whereas 15.4% did so because they suspected low milk production. Work-related causes represent the third reason of abandonment. Conclusions: Our results highlight the need to improve the health policies for the promotion, protection, and support for the initiation and maintenance of breastfeeding. In particular, our results highlight the importance of researching women’s low milk production and work-related factors, with particular emphasis on improving conciliation measures.