Malignant mesothelioma of the tunica vaginalis, a rare tumour, affects men over the age of 50 years and presents in the form of a testicular mass. It is rarely suspected preoperatively and the diagnosis is suggested by the presence of numerous nodules in the tunica vaginalis. This tumour has a high metastatic potential and raises the problem of numerous local recurrences. The diagnosis is histological with negative biological markers. Treatment is difficult; the first step must consist of surgery. The indications for radiotherapy have yet to be defined.