Lymphomatous involvement of the lungs is often a difficult clinical and radiologic diagnosis to make, yet is often critical in determining treatment. To better define the CT appearance of pulmonary lymphoma, we undertook a retrospective review of 31 patients with recurrent or secondary non-Hodgkin lymphoma or Hodgkin disease and lung parenchymal involvement on CT scans. Diagnoses were confirmed either by lung biopsy or by disease regression or progression with appropriate therapy. The CT scans were evaluated for the following findings: (1) nodules less than 1 cm, (2) a mass or masslike consolidation greater than 1 cm with or without cavitations or bronchograms, (3) alveolar or interstitial infiltrates, (4) masses of pleural origin, (5) peribronchial or perivascular thickening with or without atelectasis, (6) pleural effusions, and (7) hilar or mediastinal lymphadenopathy. The most common CT finding was a mass or masslike consolidation larger than 1 cm, seen in 21 (68%) of the 31 patients. The second most common finding was nodules less than 1 cm (19 patients). Sixty-eight percent of patients had three or more of the CT abnormalities. Lymphoma involving the lung parenchyma causes a variety of CT findings, the most common being a mass or masslike consolidation. Two-thirds of patients have more than one type of CT finding simultaneously.