Sinus histiocytosis with massive lymphadenopathy is an unusual disease characterized by prominent lymph node enlargement, especially in the cervical region. The clinical course is benign although prolonged, and no specific treatment is required. The etiology and pathogenesis are unknown. Four cases of sinus histiocytosis are reported, one in association with mediastinal lymph node enlargement and two in patients with orbital enlargement. One other patient had cervical masses. The radiologic features are reviewed to increase awareness of this entity as a cause of lymph node and orbital enlargement.