An eight-month-old boy with findings of persistent left pulmonary basal infiltrate was diagnosed with congenital unilateral pulmonary vein atresia by bronchoscopy. Cardiac catheterization documented slow left pulmonary venous return to atretic pulmonary veins. Conservative treatment was chosen because the child was asymptomatic and corrective surgery or percutaneous intervention was not technically possible. After a 3-year follow-up, the child still has no documented pulmonary hypertension. Early diagnosis of unilateral pulmonary vein atresia is important to anticipate potential threatening complications like pulmonary hypertension and hemoptysis. Surgical treatment of this entity might be drastic and complex and should be weighed against a conservative alternative and careful follow-up.