A 45-year-old woman presented in August 2005 with severe chest pain and contraction of the left hemithorax. She had been treated in 1991 for Stage IVA diffuse large B-cell lymphoma with eight courses of cyclophosphamide, adriamycin, teniposide and prednisone, followed by radiotherapy (45 Gy) delivered to the bulky mediastinal and left costo-vertebral pleural sites of involvement. Previous follow-up imaging procedures had showed only mediastinal fibrosis and a 18-fluoro-deoxyglucose positron emission tomography (PET)-negative persistent costo-vertebral pleural plaque, interpreted as scar tissue. The patient had no previous history of direct or indirect asbestos exposure. Computed tomography (CT) scanning now showed left-sided nodular circumferential pleural thickening (>1 cm). Fine needle cytology performed on the mass (A) showed atypical mesothelial cells (B, C) which gave positive immunocytochemical reactions for vimentin (D) and calretinin (E). A cytopathological diagnosis of carcinomatous mesothelioma was made and confirmed histopathologically on a pleuroscopic surgical biopsy (F). Mesothelioma should be included in the list of late sequelae of radiation therapy for lymphoma.