Mesalazine is a drug routinely used in ulcerative colitis and usually has few side effects. There have been reports of uncommon cases of severe mucocutaneous damage, such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), induced by salicylates. It is important to diagnose these promptly due to the high morbidity and mortality rates. We describe the case of a 46-year-old female with ulcerative proctitis, who developed SJS following topical mesalazine use. The lesions responded well to intravenous corticosteroids after discontinuation of the drug.