A 26-year-old muscular man was referred for evaluation of elevated serum creatinine concentration of 4mg/dL without attributable symptoms. The patient reported taking creatine supplements and ibuprofen, 800mg, before exercise. He also regularly consumed protein shakes. Two years prior, during a physical examination required for athletic participation, an elevated serum creatinine concentration (1.87mg/dL; from a baseline of 1.4mg/dL) with proteinuria (2+) but no hematuria was noted. An ultrasound showed preserved kidney size with increased medullary echogenicity, suggesting medullary nephrocalcinosis.