Disorders of coagulation and uncontrollable bleeding are major problems during a major surgical operation. The correct diagnosis, appropriate treatment and preparation for abnormal coagulation and bleeding conditions with specific factors and blood products are procedure of utmost importance. Detailed history, physical examination and performance of appropriate laboratory tests including specific factor assay are essential for the diagnosis of an abnormal coagulation and bleeding problem. We have experienced a case of factor ll deficient patient who had surgery for a glioma of the forebrain. He had a past history of two episodes of massive bleeding during operation and showed a bleeding tendency after angiography for this last admission, but he didn't show any abnormal blood coagulation tests except for a factor ll deficiency. He had received Vitamine K 20 mg/day for 7days preoperatively. All laboratory coagulstion tests became normal and he had a surgical removal of a forebrain glioma uneventfully under general anesthesia. He received only 1 unit of fresh frozen plasma during operation and had an uneventful postoperative course.