Intrathoracic involvement with cutaneous T-cell lymphoma (CTCL) was documented in eight patients with mycosis fungoides and two patients with Sĕzary syndrome. The radiographic findings consisted of multiple bilateral parenchymal nodular densities (five patients), patchy areas of consolidation (two patients), diffuse reticulonodular or interstitial infiltration (two patients), and pleural effusion without underlying parenchymal disease (one patient). Dyspnea on exertion and nonproductive cough were the most frequent presenting symptoms, and physical examination of the lungs was usually normal. In one patient a partial Pancoast's syndrome developed from a pulmonary apical mass. Results of blood gas studies and pulmonary function tests indicated an alveolar-capillary block in gas diffusion. Although the antemortem diagnosis was often suggested on cytopathologic preparations or on tissue obtained by transbronchial or percutaneous needle aspiration biopsy, a definitive diagnosis of CTCL usually required an open-lung biopsy. The response of pulmonary infiltrates to various systemic chemotherapeutic agents was variable, and the mean survival after initiation of drug therapy was 9.5 months. The findings suggest that combined modality therapy should be considered for patients with extracutaneous CTCL.