Ulcerative colitis and regional colitis Crohn are the most frequent inflammatory diseases of the large bowel in Europe. Clinical differentiation of these disorders are difficult. Diarrhoe with bloody stools are predominant. In cases with Morbus Crohn anorectal fistulas and involvement of the terminal ileum are frequently found. In cases with ulcerative colitis anorectal fistulas are more rare but in this disease a carcinoma of the colon often develops, especially when the course is severe and the involvement of the colon is extended. Clinical symptoms, courses and complications of both diseases are described. In differential diagnoses endoscopic procedures especially coloscopy play an important role. In cases of ulcerative colitis about 90% the rectum is involved. Spontaneous haemorrhage of the colonic mucosa with edema and pseudopolyps are typical endoscopic findings. Most cases with Crohn's disease show flat and irregular ulcers within a normal mucosa. In later stage a "cobble stone" relief is demonstrable. Endoscopy and guided biopsy are not only important for differential diagnosis but also for treatment and prognosis.