Malignant pleural mesothelioma has a very specific growth pattern invading the pleural surfaces and neighboring structures. For this reason precise estimation of tumor volume and description of local extension are particularly difficult. Different staging systems have been introduced, and the most widely used are discussed. Restaging of mesothelioma after induction therapy is even more complicated and still controversial. The recently described, modified response evaluation criteria in solid tumors (RECIST) criteria are presently the most accurate for response evaluation.