A 22-year-old man was referred to us with elevated plasma creatinine and anemia. He had been admitted to another hospital for fatigue and received 1 L of intravenous physiologic saline and 10 g vitamin C daily, for 7 days without improvement. The levels of plasma creatinine was 3.88 mg/dL, hemoglobin (Hb) was 10.8 g/dL, and erythropoietin was 0.90 mu/mL (reference range, 3.22-31.9 mu/mL). There was no proteinuria or hematuria. Ultrasonography showed increased kidney size and enhanced cortical echogenicity, consistent with acute kidney injury. Biopsy revealed crystal nephropathy with numerous, round basophilic crystals in the tubules, and tubular epithelium changes with flattening and simplification of the cell lining. Von Kossa staining for crystals was positive, suggesting calcium deposition. One month later, the follow-up creatinine level was 1.16 mg/dL, Hb was 15.7 g/dL, and erythropoietin was 41.99 mu/mL. Vitamin C can protect against acute kidney injury, however, high doses might cause crystal nephropathy.