Background Hyperkalemia can be harmful, but the effect of correcting hyperkalemia is sparsely studied. We used nationwide data to examine hyperkalemia follow‐up in patients with hypertension. Methods and Results We identified 7620 patients with hypertension, who had the first plasma potassium measurement ≥4.7 mmol/L (hyperkalemia) within 100 days of combination antihypertensive therapy initiation. A second potassium was measured 6 to 100 days after the episode of hyperkalemia. All‐cause mortality within 90 days of the second potassium measurement was assessed using Cox regression. Mortality was examined for 8 predefined potassium intervals derived from the second measurement: 2.2 to 2.9 mmol/L (n=37), 3.0 to 3.4 mmol/L (n=184), 3.5 to 3.7 mmol/L (n=325), 3.8 to 4.0 mmol/L (n=791), 4.1 to 4.6 mmol/L (n=3533, reference), 4.7 to 5.0 mmol/L (n=1786), 5.1 to 5.5 mmol/L (n=720), and 5.6 to 7.8 mmol/L (n=244). Ninety‐day mortality in the 8 strata was 37.8%, 21.2%, 14.5%, 9.6%, 6.3%, 6.2%, 10.0%, and 16.4%, respectively. The multivariable analysis showed that patients with concentrations >5.5 mmol/L after an episode of hyperkalemia had increased mortality risk compared with the reference (hazard ratio [HR], 2.27; 95% CI, 1.60–3.20; P <0.001). Potassium intervals 3.5 to 3.7 mmol/L and 3.8 to 4.0 mmol/L were also associated with increased risk of death (HR, 1.71; 95% CI, 1.23–2.37; P <0.001; HR, 1.36; 95% CI, 1.04–1.76; P <0.001, respectively) compared with the reference group. We observed a trend toward increased risk of death within the interval 5.1 to 5.5 mmol/L (HR, 1.29; 95% CI, 0.98–1.69). Potassium concentrations <4.1 mmol/L and >5.0 mmol/L were associated with increased risk of cardiovascular death. Conclusions Overcorrection of hyperkalemia to levels <4.1 mmol/L was frequent and associated with increased all‐cause and cardiovascular mortality. Potassium concentrations >5.5 mmol/L were also associated with an increased all‐cause and cardiovascular mortality.