Purpose: Positron emission tomography (PET) with 18-fluorodeoxyglucose (FDG) has been shown to be accurate for differentiating benign from malignant pulmonary lesions. Therefore, we evaluated the capability of FDG-PET in the characterisation of pleural lesions. Patients and methods: PET was performed in thirteen patients with pleural or intrapulmonal tumors (three with additional pleural effusion) and in three patients with aetiologically unclear pleural effusion demonstrated by CT. In all cases the diagnosis was confirmed histologically. The PET-imaging was carried out in fasted patients 50 minutes after injection of 400-670 MBq F-18-FDG without attenuation correction. Results: Twelve patients were found to have pleural or pulmonal malignomas (9 pleural mesotheliomas, 3 bronchogenic adenocarcinoma with carcinomatous pleurisy). Four patients had benign pleural changes (1 fibroma, 1 tuberculous pleurisy, 1 pleural fibrosis, 1 empyema). With FDG-PET, all 12 pleural or intrapulmonal malignomas had high FDG-uptake and were classified correctly. Due to very low or virtually deficient FDG-uptake, four histologically benign lesions were correctly interpreted as nonmalignant. Conclusion: These preliminary results suggest that FDG-PET is accurate in detecting malignant pleural tumors.