Primary superior sagittal sinus (SSS) thrombosis is an uncommon clinical entity that can be caused by a variety of local and systemic factors. The resulting morbidity and mortality vary widely depending on the extent of occlusion. Its symptoms and signs are so nonspecific that it is difficult to diagnose clinically. Sometimes it is mistaken for pseudotumor cerebri. The case in this study was inflicted with only visual symptoms. An initial computed tomographic scan only revealed brain edema. Definite diagnosis requires cerebral angiography, It is difficult to make a correct diagnosis unless we have this disease entity in mind. This case has been treated with long-term maintenance of anticoagulant for 3 years without any recurrences and adverse side effects. (Tzu Chi Med J 1996; 8: 257-261)