Patients with kidney failure depend on dialysis to maintain neutral potassium balance. The amount of potassium removed during a hemodialysis treatment is inversely proportional to the potassium concentration in the dialysis bath. Nephrologists adjust the dialysis bath potassium to account for individual variation in potassium intake among their patients. This management strategy is remarkably successful, because most patients on maintenance hemodialysis have a normal predialysis serum potassium concentration. But the serum potassium concentration of patients on maintenance hemodialysis is not constant over time; it follows a sawtooth pattern. It is this instability—especially the acute fall during dialysis—that has concerned nephrologists for decades, particularly in view of the crucial role of potassium in cardiac electrophysiology. This concern is amplified by the extraordinarily high rate of sudden death among patients on maintenance hemodialysis. In this paper, we review the safety of low-potassium dialysis and make recommendations for managing patients whose serum potassium concentration falls outside the target range.