Spontaneous lower-extremity venous thrombosis, although common in adults, is not mentioned in current pediatric textbooks. Case records from 1952 to 1972 at the Children's Hospital of Denver were reviewed, and 28 cases of venous thrombosis unrelated to local venous catheterization or venous surgery were identified. Local infection, trauma, and immobilization were the most important predisposing factors. The most frequent diagnostic findings were local tenderness and increased size of the involved extremity. Complications developed in seven of 28 cases, including three suspected cases of pulmonary emboli and three cases of staphylococcal septicemia. There was one fatality. Specific conclusions about therapy from this study could not be made. However, with venous thrombosis in children, it is recommended to identify local predisposing infections, obtain blood cultures, and treat with antibiotics when indicated.