The authors deal with the problem of mesotheliomas, their incidence and types. Most frequent are pleural mesotheliomas, which may be defined/localized/ or diffuse. Localized forms are indicated for surgery and have a favourable prognosis, diffuse forms are highly malignant and are considered a non-resectable malignity. The authors report on their own experience with a group of 47 patients with mesotheliomas. For diagnosis the part played thorocoscopy is significant.