Background: Heroin addiction is a biopsychosocial disorder and the role of some early environmental factors has also been suggested. The aim of the study was to assess whether breastfeeding may or may not affect the development of heroin addiction in adult life. Methods: We compared the incidence of breastfeeding in the first four months of life and the duration of breastfeeding in patients suffering from heroin addiction with the results for the control group. We also compared the timing of the introduction of complementary foods between the two groups. The addicted group consisted of 88 patients (27 females/61 males; mean age 22 4 years) suffering from heroin addiction, while the control group included a group of 57 healthy individuals (22 females/35 males; mean age 23 5 years). The breastfeeding history was obtained retrospectively by means of face-to-face interviews with the mothers of patients and controls. Results: The incidence of breastfeeding between 0 and 4 months was 73% (n=64) in patients with heroin addiction and 88% (n=50) in the control group. Weaning within the first 4 months of life (OR; 0.33; CI, 0.13-0.85; p=0.02) was associated with a high risk of heroin addiction in later life. Duration of breastfeeding, and the timing of the introduction of complementary foods were found to be similar in the two groups (p>0.05). Conclusions: This study suggests that early weaning (i.e. weaning during the first 4 months) may be associated with an increased risk in adult life to be faced by the offspring of parents showing heroin addiction. Duration of breastfeeding and the timing of the introduction of complementary foods (solid foods and cow's milk) might not have any effect on the development of heroin addiction.