This chapter will focus on acute colonic pseudo-obstruction, specifically addressing recent advances in clinical management. Colonic pseudo-obstruction refers to the massive dilatation of the colon with obstructive symptoms but in the absence of a mechanical cause. This can occur acutely and may be a component of ileus in which the small bowel is also dilated, or chronically, either individually, usually termed megacolon, or as part of a more generalized visceral dilatation termed chronic intestinal pseudo-obstruction. A diagnosis of acute colonic pseudo-obstruction cannot be made on the basis of bowel dilatation alone. The patient must also be clinically obstructed. Acute colonic pseudo-obstruction is a life-threatening condition in which prompt diagnosis and appropriate management can limit the occurrence of complications, for example ischemia or perforation and related morbidity and mortality. Advances, particularly in pharmacological therapy, as well as those in minimally invasive endoscopic, radiological and surgical technology will no doubt improve future management and outcome. Assessment should always include a contrast study of the colon; CT is now the most commonly employed imaging method. Patients with clinical, serological and/or radiological evidence of impending or realized cecal perforation should undergo emergency surgery. In the majority of patients unresponsive to or unsuitable for neostigmine, careful colonoscopy may effect decompression. Colonic tube placement or endoscopic colostomy should be considered if pseudo-obstruction recurs following endoscopic decompression.