Multicystic mesothelioma (MM) is a relatively rare tumour arising in the pelvic peritoneum of the tuboovarian region of young woman. Exceptionally, MM occurs on the serosal surfaces of various organs including kidney, bladder, lymph nodes, and liver. We report here the first case of MM wherein a 58-year-old woman with a previous history of endometriosis of the right ovary presented with a large multicystic mass of the spleen. The diagnosis of MM was made on a surgical specimen after splenectomy. A histopathologic examination is always necessary for the diagnosis of MM which should be differentiated from other lesions particularly from cystic lymphangioma. At one year follow-up, the patient had no evidence of recurrence. Despite the high frequency of local recurrences, MM is a benign lesion and 'en bloc' surgical excision with prolonged follow-ups is the treatment of choice.