Mediastinal lymphangioma is rare in adults, and there are few reports of their computed tomographic (CT) findings. We present the CT results in three cases of mediastinal lymphangioma. One showed a well-defined, multilocular, water-density mass enveloping mediastinal structures, without their displacement or compression; one presented as a well-defined, homogeneous, water-density mass in the right paratracheal region; and one was associated with hemorrhage into cysts and a significant increase in size over 5 years. CT is useful for diagnosis and evaluation of the extent or contents of mediastinal lymphangiomas.