Definition Hemoptysis is defined as coughing up of blood or the presence of blood in sputum. It is not a common symptom in children and although not usually life-threatening, it can become so. Massive hemoptysis is defined as bleeding that exceeds 8 mL/kg per 24 hours. Because children younger than 6 years of age tend to swallow their sputum, they rarely present with hemoptysis, unless the bleeding is substantial. Epidemiology and Etiology Causes of hemoptysis in children are listed in Table 1. Acute lower respiratory tract infection is the single most common cause, accounting for approximately 40% of cases. Hemoptysis that ranges from blood-tinged sputum to massive quantities of blood in the sputum is relatively common among those who have cystic fibrosis (CF). Massive hemoptysis is estimated to occur in 5% of CF patients, but approximately 1% will have mild hemoptysis every year, most commonly among those who are older than 18 years. In bronchiectasis due to causes other than CF, the incidence of hemoptysis is approximately 10% to 15%. Foreign body aspiration remains a leading cause of hemoptysis in children, with the majority of cases occurring in those younger than 4 years of age. Hemoptysis seldom is encountered in those who have primary pulmonary tuberculosis; it is estimated to occur in fewer than 1% of cases.