BACKGROUND Contact allergy to corticosteroids is not uncommon. As the clinical pattern that the patients exhibit may be misleading, the discovery at patch testing may be unexpected and solely a result of the fact that marker molecules for corticosteroid contact allergy are incorporated into standard series and that tests are read twice, on D3/4 and D7. OBJECTIVE We describe a patient allergic to hydrocortisone who was given a cross-reacting corticosteroid, prednisolone, that led to a systemic contact dermatitis. The patient cleared when betamethasone, a non¿Ncross-reacting corticosteroid, was administered. METHODS The patient was patch tested to a standard series including tixocortol pivalate, and an extended corticosteroid series including betamethasone. RESULTS Patch testing with tixocortol pivalate provoked an allergic patch test reaction (+? D3, +D7), whereas betamethasone did not. CONCLUSIONS Our patient's allergy was undiagnosed for 5 years, and it was not until she was given a cross-reacting corticosteroid, which led to exacerbation of her dermatitis, that her physician suspected corticosteroid allergy. The incorporation of marker molecules for the detection of corticosteroid contact allergy into standard series with two reading occasions, 3 to 4 days apart, is advocated.