A generalized skin eruption with strong itching was induced by sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, in a patient almost 6 months after initiation of the drug. Physical examination revealed a spread of skin rash from chest to back, and abdomen and thigh. Discontinuation of the drug eliminated the skin rash immediately. The emergence of new rash ended, and the rash itself withered after 1 week. The spread of the rash gradually shrank and the skin lesions subsided, leaving pigmentation 1 month later. Two months after cessation of sitagliptin, the skin eruption had subsided and oral steroid medication was stopped, but some small eczematous eruptions continued to appear intermittently. Although a drug-induced lymphocyte stimulation test was negative for sitagliptin, nonspecific radioimmunosorbent test for immunoglobulin E was increased to 532 IU/mL, with a percentage of eosinophil of 7.4%. Sitagliptin has a phenyl ring, carbonyl group, and an absorption spectrum showing three absorption peaks (199.9, 265.0, 400.1 nm), and its photosensitive mechanism could have been responsible for the itchy edematous plaque. In the present case, the initial generalized skin eruption may have been induced by an allergic reaction to sitagliptin. Close attention should be paid to patients receiving this drug with a history of urticaria, and to the development of photosensitivity.