A pulmonary thromboembolism (PTE), which is a sudden blockage in a pulmonary artery, usually due to a blood clot, is rare in children. The clinical presentation is often subtle or masked by the underlying clinical condition and the condition must be suspected during clinical testing. Although the choice of treatment depends on the clinical presentation, anticoagulation is the mainstay of therapy for children with PTE. We report the case of a healthy 1-month-old boy who presented with hemoptysis without hemodynamic instability. He was diagnosed based on chest computed tomography with angiography and 99mTc macroaggregated albumin lung perfusion scintigraphy and treated with low-molecular-weight heparin.