Introduction: Community Acquired Pneumonia (CAP) is an inflammatory pathology that damages the lower respiratory tract, usually of infectious etiology. It affects the pulmonary parenchyma producing alteration in alveolar hematosis, causing progressive hypoxemia. Objective: To determine how biological, socio-environmental, clinical radiological and analytical factors are associated with the development of CAP in children under 5 years of age hospitalized in a Public Hospital in Peru during 2019. Materials and methods: Observational, retrospective, analytical, case-control study. The sample size was made by simple, untied random sampling, obtaining 71 cases and 71 controls in the Pediatrics Service of the San José Hospital during 2019. Results: The male sex predominated in patients with CAP (54.9%); but there was no significant association between this sex and NAC (OR: 1.67 CI: 0.86-3.23, p: 0.13). The statistically significant results associated with CAP were ineffective breastfeeding (OR: 6.85, 95 % CI: 3.18-14.75) and history of respiratory diseases (OR: 5.41, 95 % CI: 2.58-11.34). Conclusions: Biological factors, ineffective breastfeeding and history of respiratory diseases are associated with CAP in children under 5 years.