A 59-year-old man was admitted to our hospital because of severe kidney failure. He complained only of general fatigue. He had no medical history and was on no medication. Urinalysis revealed no hematuria, mild proteinuria (Total protein 0.56 g/day) and hyperβ2microglobulinuria although he had no abnormal urinary findings until 6 months prior to admission. Blood tests showed anemia with a hemoglobin level of 10.5 g/dL, kidney failure with a creatinine level of 12.36 mg/dL (normal level, 0.5–1.1 mg/dL), hypocomplementemia with a C3 level of 51 mg/dL and C4 level of 3 mg/dL, an elevated serum anti-double-stranded DNA antibody level of 44 IU/mL, and hyperglobulinemia with an IgG level of 3243 mg/dL (normal level, 870–1700 mg/dL) and an IgG4 level of 621 mg/dL (normal level, 4.8–105 mg/dL). Echography and computed tomography without contrast revealed mass-like regions. Based on these findings, tumefactive lesion of IgG4-RKD was suspected, but no other intercurrent IgG4-related lesion such as pancreatitis was noted. Further imaging examinations were performed to detect diagnostic findings associated with IgG4-RKD. Ga-67 scintigraphy showed no kidney uptake. T2-weighted magnetic resonance (MR) imaging revealed multiple patchy low-intensity signals and some high-intensity signals in kidney cortex. High-intensity signals corresponded to mass-like regions. These findings were not typical for IgG4-RKD. Finally, he was diagnosed with IgG4-RKD by renal pathology with massive tubulointerstitial nephritis (TIN), characteristic fibrosis (bird’s eye pattern), and IgG4-positive plasma cell infiltrate. There was no deposition of globulin or complement in the glomeruli and no evidence of glomerular sclerosis. He received 50 mg oral prednisolone. With a subsequent decrease of serum creatinine and IgG4 levels, prednisolone was decreased by 2.5 to 10 mg every two to four weeks after induction therapy for 6 weeks. Finally he received maintenance therapy with 5 mg of prednisolone 6 months after initiation of treatment. One year after initiation of treatment, he achieved normalization of serum IgG4 level and proteinuria, and remained off dialysis with a creatinine level of 3.50 mg/dL, although severe focal atrophy developed in bilateral kidney. However, mass-like regions did not show atrophic change although renal atrophy was evident in patchy low-intensity lesions on T2-weighted magnetic resonance imaging.