Malignant mesothelioma is a rare neoplasm associated, in 80% of the cases, with exposure to asbestos fibres, with a latency period between 20 and 50 years. The treatment is palliative in most cases because of the extension of the disease at the time of diagnosis. Mesothelioma is a resistant tumour to chemotherapy and radiotherapy. Overall survival varies between 4 and 18 months, rarely over 5 years. The authors present a case of a 82-year-old man, ex-sailor, with prostatic neoplasm in hormonal "escape" phase, admitted with cough and dyspnea. The chest radiograph showed extensive right pleural effusion. The diagnostic hypothesis were metastatic, infectious and primitive neoplasm origin. Pleural biopsy revealed epithelial malignant mesothelioma confirmed by thoracoscopy, associated with prolongated occupational exposure to asbestos fibres. Without surgery indication the patient was submitted to chemotherapy with gencitabin and cisplatin associated with pleurodesis. Although he improved clinically, the presence of two malignant neoplasms, a rare situation in clinical practice, is associated with a poor prognosis, especially condicionated by the epithelial malignant mesothelioma in Butchart stage II. Finally, we discussed new differential diagnostic techniques with metastatic adenocarcinoma and target therapies under study.