THE OCCURRENCE of thrombosis, both venous and arterial, has been recognized for more than 30 years as a distinct complication of ulcerative colitis. The literature on this subject consists of individual case reports or incidental observations usually in clinical studies concerned with other aspects of ulcerative colitis.1-8 As a result, the stated incidence of this complication varies widely. The incidence of thrombosis in the larger series of cases is shown in Table 1. The occurrence of thrombosis in patients with ulcerative colitis appears predictable since many of the factors characteristic of this disease are known or believed to encourage thrombosis: toxemia, anemia, emaciation, prolonged rest in bed, and frequent surgical procedures. However, as early as 1936, Bargen and Barker,2 as a result of their observations on the extensive propagation of such thrombi, considered the possibility that an increased coagulation tendency of the blood occurs in patients with ulcerative