Acetazolamide-induced central nervous system toxicity occurred in two patients undergoing hemodialysis. Symptoms of toxicity included fatigue, lethargy, and confusion, which resolved several days after discontinuing acetazolamide. Pharmacokinetic studies showed markedly elevated serum concentrations of the drug during the period of toxicity, which decreased at a slower rate compared with that reported in patients with normal renal function. The effect of hemodialysis on acetazolamide clearance was quantified. The agent should be avoided in patients receiving dialysis unless the dosage is reduced and serum concentration monitoring can be performed in a timely manner. These patients should be monitored closely for central nervous system toxicity if acetazolamide is given.