The unilateral absence of one pulmonary artery is a rare congenital abnormality. The authors report a clinical case of a two-year-old boy with no previous medical history who was referred for evaluation after the detection of pulmonary asymmetry on the chest X-ray with a right mediastinal shift. The CT scan and pulmonary perfusion scintigraphy pointed to an absent right pulmonary artery, which was confirmed by right heart catheterization and cardiac magnetic resonance imaging. This is an important pathology because early diagnosis and timely correction can prevent future complications. Since at this time the patient is asymptomatic, the authors opted for careful clinical vigilance.