The intestinal lesion of Behcet's colitis shows aphthoid or punched-out ulceration. However, the diagnosis of Behcet's colitis should be based on the presence of other stigmata of Behcet's syndrome, since these morphological characteristics are not pathognomonic by themselves. Furthermore, the stigmata of Behcet's syndrome could appear simultaneously or separately with intervals of several months to years. Besides, when a physician first meets patients with intestinal ulcerations of aphthoid or punched-out shape, if they do not have any stigma of Behcet's syndrome, the physician has some difficulty in making a diagnosis of Behcet's colitis. The purpose of this retrospective study was to investigate the followings: 1) The upgrade in clinical type of Behcet's colitis with the advance of time. 2) What portion of the patients with aphthoid or punched-out ulcerations, but without any other clinical feature of Behcet's syndrome, could be diagnosed as Behcet's colitis with the advance of time? During the mean follow-up period of 38.2 months, 4 (22.2%) out of 18 patients with Behcet's colitis upgraded their clinical types. In the nonspecific ileocolitis group, who had no major stigma of Behcet's syndrome on their initial visit, 3 (30%) out of 10 patients were subsequently diagnosed as Behcet's colitis during the mean follow-up period of 33.3 months. From these results, we could conclude that in possible or suspicious cases of Behcet's colitis, a more confident diagnosis could be made by close observations for new developments of major stigma of Behcet's syndrome. Even in cases of nonspecific ileocolitis, the diagnosis of Behcet's colitis could be made in a significant number of cases as time goes by.