Mannitol is an osmotic diuretic widely used in the diagnosis and prevention of acute oliguric renal failure, acute cerebral edema and acute glaucoma. Mannitol, though ordinarily a benign substance, may accumulate in renal failure with potentially deleterious consequences. Mannitol intoxication is ordinarily characterized by confusion, lethargy, stupor, and if severe enough, coma. The use of mannitol in renal failure has rarely been associated with a worsening of the preexistent renal dysfunction. We report a case of acute oliguric renal failure solely attributable to mannitol administered in the course of therapy for acute glaucoma.