Little is known about the frequency and patterns of hyperkalemia in clinical settings. We evaluated the association between baseline antihypertensive medications that may affect potassium levels (angiotensin converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), beta-blockers, loop/thiazide diuretics, and potassium-sparing diuretics) and hyperkalemia, defined by potassium >5 mEq/L and >5.5 mEq/L, over a 3-year time period in 194,456 outpatients in the Geisinger Health System, as well as actions taken after an episode of hyperkalemia. The proportions of patients with 0, <2, 2–4, and ≥4 potassium measurements per year were 20%, 58%, 16%, and 6%. Potassium levels >5 mEq/L and >5.5 mEq/L occurred in 10.8% and 2.3% of all patients over the 3-year period; among patients with ≥4 measurements per year, corresponding values were 39.4% and 14.6%. Most cases of hyperkalemia occurred only once during follow-up. The antihypertensive medication class most strongly associated with hyperkalemia was ACEIs. Among patients with a measurement of potassium >5.5 mEq/L, only 24% were seen by a nephrologist and 5.2% were seen by a dietician during the 3-year period. Short-term actions after a potassium measurement >5.5 mEq/L included emergency room visit (3.1% within 7 days), re-measurement of potassium (44.3% with 14 days), and change in a potassium-altering medication (26.4% within 60 days). The most common medication changes were discontinuation/dose reduction of an ACEI/ARB or potassium-sparing diuretic, which occurred in 29.1% and 49.6% of persons taking these medications, respectively. In conclusion, hyperkalemia is common. Future research may enable optimal RAAS inhibitor use with improved management of hyperkalemia.