Acute colectasia may occur in patients under mechanical ventilation. Causative factors include haemodynamic changes, potassium loss, underlying pathology (chronic respiratory failure, cirrhosis) and especially morphine-like compounds used for sedation. Analysis of the results obtained with various treatments suggests that surgery is not justified: caecal perforation is extremely rare in a previous healthy colon; any surgical procedure is hazardous in this type of patient, and colectasia frequently regresses under appropriate medical treatment, even though mechanical ventilation is pursued.