Lymphangiomas are very rare benign tumours, believed to arise from congenital malformations of the lymphatic system. They grow very slowly, but are capable of massive expansion and infiltration of the surrounding tissues. If left untreated they can cause serious and sometimes fatal complications. The thorax is commonly affected, with involvement of the ribs, pleura, pericardium, lung parenchyma, mediastinum and vertebrae. Treatment depends on the extent of the disease. While local excision is the treatment of choice for localized lesions, radiotherapy is used for more extensive disease. In this report we describe three patients with extensive thoracic lymphangiomatosis who were treated successfully with irradiation alone. The value of early diagnosis and treatment is emphasized.