We present a patient with schizophrenia who developed dexmedetomidine-induced polyuria after superficial parotidectomy. Two hours after starting the dexmedetomidine infusion, urine output increased from a baseline rate of 80 mL/h to a 7-hour average rate of 400 mL/h (range, 280-560 mL/h), the serum sodium concentration increased from 132 to 139 mEq/L, and urine-specific gravity was 1.006. Following dexmedetomidine discontinuation, the urine output decreased to an average of 66 mL/h (range, 40-100 mL/h). Close monitoring of urine output and serum sodium concentration may be indicated during dexmedetomidine infusion.