The diagnosis of malignant mesothelioma can pose several problems to the surgical pathologist first the morphological appearances of the tumour are known to be diverse with mimicry of a range of both reactive and neoplastic conditions. The diagnosis of malignant mesothelioma relies firstly on the identification of the mesothelial nature of the neoplastic cell and secondly on the demonstration of the invasive properties of the proliferation. Histopathology is the largest specialty within pathology mesothelioma cytology examines single cells often through analysis of bodily fluids for mesothelioma patients this fluid most commonly is either pleural effusion in pleural malignant mesothelioma patients or peritoneal effusion for those with mesothelioma of the peritoneum. Malignant mesothelioma malignant mesothelioma also mesothelioma is a form of cancer it arises from the mesothelium it should not be confused with benign multicystic mesothelioma and benign papillary mesothelioma