Hospital admissions for hyperkalemia had been climbing slowly from 1994 (2.4/1000) through 1999 (4.0/1000), but increased nearly threefold to 11/1000 by late 2001 (P < .001). The rate of hyperkalemia associated with in-hospital death rose gradually between 1994 (0.3/1000) and 1999 (0.7/1000), but increased nearly threefold after publication of the RALES to 2.0/1000 in late 2001 (P < .001). Patients treated with spironolactone were on average 13 years older than patients in the RALES. There were equal numbers of men and women. Most patients were also taking loop diuretics, and more than half had been hospitalized for heart failure within the previous month.