Four cases of Stevens-Johnson syndrome considered to be induced by methazolamide were reported. In all of the cases, the first signs of Stevens-Johnson syndrome (i.e., swelling of the skin and mucous membranes or slight fever) appeared about 2 weeks after the patient started taking methazolamide (75 or 100 mg/d). After the appearance of erythema, the skin and mucous membrane lesions progressed rapidly and spread over the entire body, even after the patient ended methazolamide treatment and started treatment with prednisolone. During prednisolone treatment, the skin and mucous lesions became bullous, ruptured spontaneously, and dried with crust or erosion. HLA typing was positive for HLA-B59 in 3 of 4 cases. Methazolamide should be prescribed with caution in patients of Japanese or Korean descent.