The role of ultrasound scanning in the diagnosis of cancer of the colon under emergency conditions such as intestinal obstruction, perforation or, more rarely, heavy colonic bleeding, is discussed. In any case, ultrasound scanning can quickly and rationally indicate choices for further assessment when possible. Characteristic ultrasonic images are described, and possible differential diagnoses are discussed briefly. The method seems significantly sensitive, although nonspecific, as it can give analogous images in cases of inflammatory pseudo-tumors, Crohn's disease, and adult intussusception.