Globally, Acute Lymphoblastic Leukemia (ALL), represents more than 30% of all types of cancers in children aged between 0 and 9 years. In Peru, it has not been evaluated whether exclusive breastfee-ding (EB) is a protective factor for ALL. Objective: To identify the protective and risk factors associated with acute lymphoblastic leukemia in children aged between 0 and 13 years in a national hospital in Lima, Peru. Patients and Method: Observational, analytical study, case-control design. 112 cases diagnosed with ALL and 229 controls were evaluated. The data were collected by interviews with the mothers of both groups. The magnitude of the association between ALL and EB was estimated using the odds ratio (OR) and multivariate logistic regression in Stata v 12. Results: 50.9% (57/112) of the cases and 51.5% (118/229) of the controls were male. The mean age of the cases was 6.7 ± 3.2 years and of the controls 5.7 ± 3.5 years. The mean age of the mothers of the cases was 35.9 ± 6.5 and of the controls was 34.1 ± 7.1 years. EB reduces the risk of ALL by 44% compared with those who did not receive it, OR 0.56, p = 0.017, 95% CI (0.35-0.90). Complete secondary education reduces the risk of ALL by 62%, OR 0.38 CI 95% (0.15-0.61). Conclusions: Exclusive breastfeeding and the mother’s complete secondary education are protective factors for the development of ALL in children and adolescents.