Keratoacanthomas (KAs) in 14 patients were treated with 20% fluorouracil ointment, two or three times daily, for two to four weeks. All lesions responded promptly and cleared in an average period of 3.4 weeks (range, one to seven weeks). Allergic contact dermatitis to fluorouracil occurred in two patients. This treatment response suggests that topical application of fluorouracil ointment is an effective alternative to conventional methods of treating KA.