OBJECTIVE: Lymphangiomas are rare benign tumors most often seen in childhood. When they occur in adults, radiologic diagnosis can be difficult. A retrospective study of the CT and MR appearances of thoracic lymphangiomas in adult patients was performed in order to describe the range of radiologic features of these tumors. MATERIALS AND METHODS: Cases of adult lymphangioma at three institutions were identified in the records of 19 patients, predominantly female, 18-67 years old. RESULTS: The most common CT appearance was a smoothly marginated cystic mass. Unusual features included calcification, spiculated margins, and homogeneous soft-tissue attenuation. The majority of cases were located in the anterior or superior mediastinum. Unusual locations included the pericardium, pulmonary hilum, and pulmonary parenchyma. Signal characteristics on MR images varied. CONCLUSION: The radiographic appearance of lymphangiomas in the chest in adult patients is varied. The diagnosis cannot be suggested on the basis of radiologic studies alone.