Introduction : Demons Meigs is a rare, anatomo-clinical syndrome associated, with a benign ovarian tumor, ascitis and hydrothorax. The interest assigned to this triad reside in its simularity to the malignant ovarian tumor in its advenced stage and in its perfect and definitive surgical curability. Observation : The authors report here a case of 65 years old female patient, who were consulted for hypogastric pains and signs of vesical compression. Clinical examination showed a well defined hypogastic mass, rounded in shape measured 15cm diametr in a moderately abundant ascitis. The abdomino-pelvic echographic examination, showed a left heterogenic ovarian mass associated with intra peritoneal effasion. Chest X-Ray showed right hydrothorax. As the general condition was conserved, diagnosis of Demons-Meigs syndrome was evoked . This diagnostic was confirmed in the preaperative period by the presence of an ovarain mass without macroscopics malignants signs of malignancy, also histoulogical examination showed benign fibroma. Asimple excision was sufficient to have a definite recovery without recurrence six years after the operation. Conclusion : The association of pleural effusion and an ovarian tumour is not synonymous of metastasic invasion. Demon Meigs syndrome must be evoked because the surgical excision of the ovarian tumour permits the definitive recovery without complementary treatment.