THE RECENT controversy concerning the relationship of adenomatous polyps and colonic carcinoma has stimulated renewed interest in the detection of polypoid tumors of the colon (1-4, 8). Air-contrast barium-enema studies have proved the most productive diagnostic method (7). With these, however, a myriad of colonic defects are seen, only a few of which are significant (11). In this report, we shall outline a method of differentiating true polypoid tumors from extraneous material, such as air bubbles, fat, feces, mucous strands, and foreign bodies. The material for this report has been collected from 21,043 aircontrast barium-enema examinations performed according to the Welin modification at the Allmanna Sjukhuset in Malmo, Sweden, between Dec. 1, 1953, and June 30, 1962. The particulars of the method have been described elsewhere (7). Roentgen Features of Different Types of Polyps True polypoid tumors of the colonic mucosa are attached to the bowel wall by a base which is an integral part of the mucosa itself. When this base is demonstrated, the radiologist may be certain that he is dealing with a true polypoid tumor instead of with foreign matter, which does not have an attachment to the mucosa. Polypoid tumors of the bowel arise as fiat plaques of tissue which spread circumferentially (Fig. 1, A). The more rapidly infiltrating tumors soon invade the deeper layers of the bowel wall and encircle the bowel until the typical "napkin ring" carcinoma is produced. The slower growing, noninfiltrating adenomatous polyps have a different natural history. Here the plaque of adenomatous tissue is lifted up and drawn out by the traction of the fecal stream until a typical stalk or peduncle is formed (Fig. 1, C). An intermediate form of polyp exists in which the adenomatous tissue forms a broad-based protuberant mass (Fig. 1, B). In this type the process of traction has not progressed long enough to produce a pedicle, but on cross section a central fibrous core representing a potential stalk is usually present in the midportion. By means of this convenient explanation of tumor growth, polypoid colonic tumors can be divided into three morphologic groups: (a) sessile, (b) intermediate, and (c) pedunculated. Each type has its own characteristic roentgen picture, depending on the appearance of the base of the polyp. Some authors (6) do not agree with this concept of the passive production of a pedicle, but it is of value in explaining the formation of the three different roentgen images. The sessile polyp is fiat and difficult to separate from the wall. Close scrutiny of the bowel wall is necessary, much as when searching for a fissure fracture in the cortex of bone. These fiat tumors are the most difficult to separate from infiltrating carcinomas or from adherent fecal material.