Pseudoobstruction of the colon is a specific variety of adynamic ileus. Its characteristic clinical presentation is severe cramping lower abdominal pain, a massively distended abdomen, and a characteristic x-ray picture. Thirty-five patients with this disease complex have been reviewed, and their surgical and medical therapy is discussed. Guidelines for continued medical versus surgical intervention are suggested. Two patients underwent decompression with the colonoscope. Its use and a possible hazard of the procedure are discussed. For those patients who develop pseudoobstruction after trauma or surgery, a pathophysiologic explanation is offered. The possible role of prostaglandin abnormality in the genesis of pseudoobstruction is also discussed.