A 74-year-old man who had been administered trimethoprim-sulfamethoxazole for three weeks suffered from drug-induced hypersensitivity syndrome/drug rash with eosinophilia and systemic symptoms (DIHS/DRESS). In the early stage of the clinical course, he developed renal dysfunction. A renal biopsy showed granulomatous tubulointerstitial nephritis accompanying the proliferation of human herpes virus ( HHV)-6 in tubular epithelial cells. With corticosteroid therapy, the systemic rash and renal function gradually improved. The present patient is the second case of DIHS/DRESS demonstrating a possible reactivation of HHV-6 in the renal tissue. The clinical role of viral reactivation in DIHS/DRESS must be further elucidated.