Severe eating disorders characterized by repetitive episodes of purging and vomiting can occasionally trigger acute kidney injury. However, interstitial nephritis induced by episodes of repeated vomiting has rarely been reported, and the pathophysiology of this entity remains unknown. A 26-year-old man was admitted to our hospital because of known hypokalemia. His serum electrolyte profile showed: sodium 133 mEq/L, potassium 2.6 mEq/L, chloride 72 mEq/L, total carbon dioxide 50 mEq/L, blood urea nitrogen/creatinine ratio (BUN/Cr) 21.9/1.98 mg/dL, and magnesium 2.0 mg/dL. Arterial blood gas analysis showed: pH 7.557, partial pressure of carbon dioxide 65.8 mmHg, and bicarbonate 58.5 mEq/L. His urinary potassium concentration was 73.2 mEq/L, and Cr was 111 mg/dL. Renal biopsy revealed acute tubular necrosis and tubulointerstitial nephritis with a few shrunken glomeruli. Repeated psychogenic vomiting may precipitate acute kidney injury and interstitial nephritis secondary to volume depletion and hypokalemia. Serum electrolyte levels and renal function should be carefully monitored in patients diagnosed with eating disorders to prevent tubular ischemia and interstitial nephritis.