Toxic megacolon belongs to the severe acute complications of inflammatory bowel diseases. The frequency is 1.6-21.4% among patients with ulcerative colitis and 0.3-2% in those with Crohn's disease. The main characteristics of toxic megacolon are toxemia, sepsis and distension of the colon due to the diminished muscular tone, loss of motor activity and increased amount of colonic gas. Sepsis and/or perforation of the large bowel can complicate this situation. The most important diagnostic procedure is the abdominal X-ray. Should the diameter of colonic distension exceed 60 mm, the diagnosis of toxic megacolon has been confirmed. Conservative treatment of toxic megacolon consists of water and electrolyte replacement, total parenteral nutrition, administration of corticosteroids and broad-spectrum antibiotics and repeat patient's prone positioning. If medical therapy is not successful during the first 72 hours, surgical intervention is indicated. The most common procedure is subtotal colonic resection with creation of an ileostomy. Patients with toxic megacolon should be managed at specialised centers, where cooperation of experienced gastroenterologists, surgeons and intensive care experts is possible.