For the differential diagnosis between fibrous pleuritis and other malignancies such as lung cancer, multiple immunostaining is essential to diagnose pleural mesothelioma. For cytological diagnosis of pleural effusions, differentiation between mesothelioma cells and reactive mesothelial cells is very difficult. Therefore, histological diagnoses of tumor tissues obtained via biopsy are essential. To diagnose epthelioid mesothelioma, more than 2 positive and negative markers must be consistent with those known for mesothelioma. To diagnose sarcomatoid mesothelioma, keratin is usually positive, differentiating the diagnosis from that for real sarcoma. For surgical treatment for pleural mesothelioma, extrapleural pneumonectomy (EPP) and pleurectomy/decortication (P/D) are usually performed. The proportion of P/D increases because of the low death rates with surgery and similar survivals. However, a trimodal approach, such as EPP with chemotherapy and radiotherapy, is best for longer survival and expected to be curative. For chemotherapy, only cisplatin (CDDP) combined with pemetrexed (PEM) is effective, and no other agents have been identified for this disease. Nowadays, clinical immunotherapy trials start with phase II study.