Lichen planus is a recognized complication of sulfasalazine therapy. Two patients developed typical oral and cutaneous lichen planus on sulfasalazine and their skin lesions recurred when they were subsequently changed to mesalazine. Lichen planus only resolved on withdrawal of both drugs. It seems likely that the aminosalicylic acid moiety is responsible for this reaction and that lichen planus is a true complication of mesalazine therapy.