This controlled clinical trial, conducted in southern Brazil, assessed the impact of paternal inclusion in a breastfeeding education program carried out in a maternity hospital. Rates of breastfeeding in the first 6 months of babies' lives were measured in 586 families: 201 in the control group, 192 in the group with only mothers exposed to the intervention, and 193 in the group with mothers and fathers exposed to the intervention. Paternal inclusion significantly increased the rates of exclusive breastfeeding but not the rates of any breastfeeding. Intervention with fathers with less than 8 years of schooling resulted in a decrease in the rate of breastfeeding when compared with the intervention with mothers only. The likelihood of success might have been greater if the cultural and behavioral complexities associated with this practice had received more attention.