Aminosalicylates (5-ASA, sulfasalazine and mesalazine) play a central role in the treatment of ulcerative colitis (UC). For acute treatment of mild to moderate flares and in maintenance treatment, their efficacy has been established. Since ulcerative colitis is limited to the distal colon in two thirds of the patients, topical therapy also plays an important role. In mild/moderate active disease 5-ASA 4 g/d is as effective as oral corticosteroids. Ulcerative proctitis is treated with 2 x 500 mg or 1 x 1 g suppositories and proctosigmoiditis with 1 to 4 g enemas. Oral 5-ASA is also safe in maintenance treatment and is generally well tolerated. The risk of colorectal tumours is increased in patients with longstanding ulcerative colitis and epidemiological evidence indicates that chronic 5-ASA treatment reduces this risk. However, at present there is insufficient evidence to maintain patients on life-long 5-ASA maintenance treatment for this indication.