The early diagnosis of mesothelioma rests on very common clinical evidence, including pleuritis of recent onset, history of contact with asbestos, chest pain, often moderate loss of weight and slight changes in old pleural fluid cytology, 24% for Adams' needle biopsy and 93% for thoracoscopy, where the only negative results are obtained in patients with adhesive pleuritis. Prognosis depends on several factors, the most favourable ones being the histological type of the lesion (epithelial or mixed), the fact that it is limited to the parietal or diaphragmatic pleural and, on the patient's side and accessorily: female sex, lack of exposure to asbestos, age under 50, good general condition and absence of chest pain.