Hydrochlorothiazide is a diuretic drug used in the treatement of edema and hypertension. We report a case of hydrochlorothiazide induced photosensitivity in a 54 year old woman who had taken hydrochlorothiazide for 3 years for hypertension. She complained of itching and burning sensation with erythematous papules and lichenified plaques on light-exposed areas. Fhototest showed marked decrease of the minimal erythema dose(MED) for UVA. The symptoms subsided after the use of topical steroid and the substitution atenolol for hydrochlorothiazide. (Kor J Dermatol 1992; 30(3): 373-376)