INTRODUCTION: Positron emission tomography (PET) has a clear role in oncology, particularly in thoracic disease. In the light of our experience and a revue of the literature we define precisely the role of metabolic imaging in the diagnosis of pleural pathology. BACKGROUND: In particular PET allows characterisation of malignant pleural disease and provides prognostic information in mesothelioma. Metabolic imaging provides clinical information for the staging of pulmonary cancer, in the search for a primary tumour in metastatic pleurisy and also in the follow up of chronic or recurrent pleural pathology. CONCLUSIONS: It is justified, therefore, that PET joins the diagnostic armamentarium of pleural pathology, solid or liquid.