Sixteen episodes of a distinctive, papular rash occurred in eight patients following withdrawal of 6-mercaptopurine (6MP) and methotrexate (MTX) used as maintenance therapy for acute lymphoblastic leukemia (ALL). The rash also developed in one of the eight patients when only 6MP was discontinued. The eruption occurred mainly on the face, and in this site resembled the perioral dermatitis seen following withdrawal of topical fluorinated steroids. The rash generally began within 3 weeks of stopping 6MP and lasted 3 to 4 weeks. It failed to improve with the use of topical corticosteroid. We conclude that this rash is caused by the withdrawal of oral 6MP.