Acute interstitial nephritis is an infrequent cause of early allograft dysfunction. Prophylactic trimethoprim sulfamethoxazole (cotrimoxazole) is frequently prescribed early in the course of kidney transplantation. Herein we have reported a case of delayed graft function associated with eosinophilia in which the renal biopsy showed interstitial mononuclear infiltrates with abundant eosinophils. An initial methylprednisolone course failed to lower the serum creatinine, but renal function and eosinophilia persistently improved following cotrimoxazole withdrawal and a second course of steroids. Cotrimoxazole acute interstitial nephritis is an infrequent but treatable cause of kidney allograft dysfunction, which should be included in the differential diagnosis of delayed renal allograft function.