A case of malignant peritoneal mesothelioma mimicking mesenteric inflammatory disease (MID) is presented. The patient had mesenteric and omental lesions characterized at biopsy by extensive fibrosis of fat tissue with mild to moderate inflammation. One year later, post-mortem examination revealed a well-differentiated epithelial mesothelioma. Immunohistochemical stains for keratin and vimentin were diffusely positive, whereas EMA showed a membranous staining of scattered cells. CEA, Ber-EP4, B72.3 and Leu-M1 were negative. In addition, actin monoclonals decorated groups of cells pertaining to the tumoural component. Immunostains of sections from retrieved paraffin blocks of the previous biopsy showed that the bulk of the spindle-shaped and histiocytic-like cells present in the fibrous streams was strongly labeled by low-molecular-weight keratin, and coexpressed vimentin and actin. EMA showed a membranous staining of sporadic spindle and round cells. The other immunostains were invariably negative. This immunohistochemical pattern closely corresponded to the immunophenotype of the mesothelial tumour detected at autopsy and was very suggestive of myofibroblastic/submesothelial cell origin. The quantitative evaluation of silver nucleolar organizer regions (Ag-NORs) demonstrated high levels of cell proliferation in both surgical and autopsy tissue samples.