Mannitol overuse-induced acute renal failure (ARF) has rarely been described. We report four cases, all male, between the ages of 20 and 42 years, who developed acute renal failure (3 anuric, 1 nonoliguric) after receiving mannitol 1,172 ± 439 g (mean ± SD) during a time period of 58 ± 28 h. The infusion rate was 0.25 ± 0.02 g/kg/h. The onset of acute renal failure was detected 48 ± 22 h after infusion. In 2 of the 3 cases in which urinary cytology was evaluated, the presence of vacuole-containing renal tubular cells was observed. All patients had hyponatremia (120 ± 11 mEq/l), and hyperosmolality (osmolar gap 70 ± 11 mosm/kg water). No other factors could be pointed to as causing acute renal failure. In the 3 anuric cases in which hemodialysis was performed, immediate recovery of diuresis was observed. Two patients recovered renal function on the fifth and sixth days, and 2 died due to endocranial hypertension – one of them while recovering – on the fourth and sixth days. In the present report, mannitol-induced ARF occurred at clustered doses of 0.25 mg/kg/h.