Abstract
Summary Proved diagnosis of a malignant or a premalignant tumor of the large bowel is recorded in 89 patients who for more than one year previously had been observed while a diagnosis of diverticulosis or diverticulitis of the colon had been accepted as the cause of gross rectal bleeding. In the experience here reported, rectal bleeding which might have been considered attributable to diverticulosis or diverticulitis of the colon has ultimately been proved to have been due to neoplastic disease four times out of five.