We present the case of a 37-year-old male, admitted to our clinic with abdominal tenderness, right supraclavicular tumour, and ascites. The presence of ascites was incidentally reported 6 years before, but no other evaluation was done at that moment or during this period. Abdominal ultrasound and CT scan revealed moderate ascites, perivascular adenopathies, and multiple abdominal cystic lesions, while thoracic CT scan revealed the same lesions in mediastinum. Laboratory data were within normal limits, including the tumoral markers, and the tests for hydatid cysts. A biopsy from the right supraclavicular nodule was performed, and based on usual and immunohistochemical stains (calretinin, mesotheline, CK 5/6, CK 7, CK18 diffusely positive in mesothelial cells, and CEA -M, bcl-2 and vimentin negative), suggested the diagnosis of mesothelioma. Based on these results, the diagnosis of "multicystic mesothelioma" was made. The patient was referred for surgery.