The authors make a review of literature and present the results of the spinal fluid test in 12 cases of epidemic mumps complicated by meningitis. The spinal taps were performed for diagnosis and treatment (decompression) ; all patients had symptoms and clinical signs of acute meningitis. The authors found the following average type of spinal fluid: aspect, lightly opalescent; no color; fibrin clot; initial pressure 19 cm of water; 570 cells/cm (95 per cent), lymphomononuclear, 3 per cent, polymorphonuclear, 2 per cent, plasma cells; 41 mgm/100 ml of total protein; Pandy test ++; Weichbrodt test negative; Nonne test +; colloidal benzoin 00000.02222.-00000.0; Takata-Ara test negative; 705 mgm/100 ml of chlorides; 62 mgm/100 ml of glucose; serological tests and bacteriological tests negative. The authors make general considerations on the differential diagnosis, particularly with tuberculous meningitis.