A comparative study was performed between plain abdominal films of 110 patients with neoplasms of the large bowel and 52 normal subjects for control. In neoplasms of the right colon the failed spontaneous visualization of caecum and ascendent colon or the direct recognization of lume's deformation allow us to suspect such a lesions in about 90% of the cases. Neoplasms of the other tracts of the large bowel may be suspected only when plain abdominal film demonstrates direct evidence of an obstruction: in about 25% of the cases.