Intrathoracic non-Hodgkin's lymphoma (NHL) usually presents with roentgenographic evidence of mediastinal lymph node enlargement, pulmonary masses, pleural effusion, and a clinical picture of a systemic disease with lymphadenopathy. The presentation of NHL with pleural effusion as the major roentgenographic abnormality and no clinical peripheral lymphadenopathy or organomegaly is unusual. During a seven-year period, we encountered 19 patients with NHL in whom pleural effusion was the major roentgenographic and clinical finding. Pleural fluid cytologic results were diagnostic in only two patients. Closed pleural biopsy was positive in three. Eight of 11 patients had diagnostic immunophenotypic lymphocyte cell marker studies. Seven of nine patients had diagnostic thoracoscopy and one thoracotomy. The CT scan identified biopsy sites when pleural fluid and tissue studies were nondiagnostic. Lymphomatous tissue was obtained from the pleura in 17 of the 19 patients supporting the contention that pleural effusion in patients with NHL is usually due to pleural lymphoma rather than obstruction to mediastinal lymphatics.