OBJECTIVE: To identify the impact of training in breastfeeding on knowledge, skills, and professional and hospital practices. DATA SOURCE: The systematic review search was carried out through the MEDLINE, Scopus, and LILACS databases. Reviews, studies with qualitative methodology, those without control group, those conducted in primary care, with specific populations, studies that had a belief and/or professional attitude as outcome, or those with focus on the post-discharge period were excluded. There was no limitation of period or language. The quality of the studies was assessed by the adapted criteria of Downs and Black. SYNTHESIS OF DATA: The literature search identified 276 articles, of which 37 were selected for reading, 26 were excluded, and six were included through reference search. In total, 17 intervention articles were included, three of them with good internal validity. The studies were performed between 1992 and 2010 in countries from five continents; four of them were conducted in Brazil. The training target populations were nursing practitioners, doctors, midwives, and home visitors. Many kinds of training courses were applied. Five interventions employed the theoretical and practical training of the Baby-Friendly Hospital Initiative. All kinds of training courses showed at least one positive result on knowledge, skills, and/or professional/hospital practices, most of them with statistical significance. CONCLUSIONS: Training of hospital health professionals has been effective in improving knowledge, skills, and practices