Abstract A 40-year-old woman who had bilateral swelling in the eyelids and submandibular region was admitted. Clinical findings suggested she had primary Sjogren's syndrome. Laboratory data showed glucosuria, positive CRP (0.50 mg/dl), liver dysfunction (AST 53 U/l, ALT 101 U/l, γ-GTP 241 U/l, ALP 914 U/l, LAP 496 U/l), hyperglycemia, hypergammaglobulinemia (IgG 3450 mg/dl, IgA 91 mg/dl, IgM 80 mg/dl), hypocomplementemia (C3 73 mg/dl, C4 2 mg/dl, CH50 < 19.0 U/ml), renal tubular dysfunction (urine N-acetyl-β-d-glucosaminidase 8.6 U/l, urine _β2-microglobulin 83 μg/l), and urinary concentration defect. Ammonium chloride loading test was normal. Gallium-67 scintigram indicated abnormal uptake in bilateral lacrimal glands, submandibular glands, and kidneys. A diagnosis of Mikulicz's disease and interstitial nephritis was made, since biopsy specimens of her lacrimal gland and minor salivary gland showed diffuse infiltration of lymphocytes. Renal biopsy specimens also showed severe interstitial infiltration of lymphocytes. Symptoms and laboratory data normalized in response to methylprednisolone pulse therapy and prednisolone 60 mg/day. This case of Mikulicz's disease complicated with interstitial nephritis was successfully treated by high-dose corticosteroid.