BACKGROUND: Acute cor pulmonale is a clinical syndrome with signs of right-sided heart failure resulting from sudden increase of pulmonary vascular resistance. CASE PRESENTATION: A five-year-old male, infected by human immunodeficiency virus (HIV), was admitted at the division of infectious diseases of this hospital with cough, tachydyspnea, fever, and breathing difficulty. Computed tomography scan showed ground-glass opacities, cystic lesions, and bronchiectasis. The patient had nasal flaring, intercostal and subcostal retractions, and keeled chest. Abdomen was depressible; liver was 3 cm from the right-costal border, while spleen was 6 cm from the left-costal border. Echocardiogram examinations showed signs of acute cor pulmonale characterized by pulmonary hypertension and increased right-heart chamber dimensions. DIAGNOSTICS OUTCOME: Acquired immunodeficiency syndrome (AIDS)-B3, lymphocytic interstitial pneumonia (LIP), and acute cor pulmonale. Regressions of pulmonary hypertension and of right-heart chamber were observed after 30 days of highly active antiretroviral therapy (HAART) and chloroquine therapy. CONCLUSION: AIDS should be considered in children with recurrent pneumonia that is mostly associated with LIP rather than cystic fibrosis.