ABSTRACT Introduction In patients with incident end-stage kidney disease (ESKD), hyperkalemia (HyperK) is a common indication for initiating kidney replacement therapy (KRT). Hemodialysis (HD) and peritoneal dialysis (PD) both effectively reduce serum potassium, but HD is often considered superior due to its perceived faster efficiency. However, evidence supporting this perception remains limited. We hypothesized that HD and PD would be equally effective for the management of severe HyperK during hospitalization. Methods We conducted a prospective cohort study at the Nephrology Department of Hospital Civil de Guadalajara. Consecutive, dialysis-naïve patients hospitalized with ESKD and severe HyperK (serum potassium >6.5 mEq/L at admission) between 2022 and 2024 were included. The modality of KRT (HD vs PD) was determined by the treating nephrology team. The primary outcome was the trajectory of serum potassium reduction between groups. Secondary outcomes included daily potassium trajectory, catheter dysfunction, length of stay and mortality. Results Eighty-two patients were included: 34 initiated PD, 37 HD and 11 received conservative management. Baseline demographic and clinical characteristics were similar across groups (P > .05). Median age was 65 years [interquartile range (IQR) 53–74], with diabetes in 33% and hypertension in 53%. Median admission potassium was 6.99 mEq/L (6.7–7.6), serum creatinine 15.9 mg/dL (11.5–23.1) and estimated glomerular filtration rate 2.91 mL/min/1.73 m² (1.80–4.09). The PD group underwent a mean of 45 (±15) exchanges during hospitalization, and the HD group received 4.6 (±1) sessions. Serum potassium decreased similarly in both groups (P > .05), with substantial reductions on Day 1 (PD 6.03 mEq/L; HD 5.90 mEq/L) and stabilization by Day 5 through Day 15. Catheter dysfunction occurred in 11% of patients, with similar rates between groups, hospitalization median was 5 days (IQR 3–8) and 12-month mortality was 26.8%, without differences between modalities. Conclusions In this prospective cohort of ESKD patients with severe HyperK, both PD and HD achieved comparable potassium reduction and clinical outcomes, supporting PD as an effective alternative for urgent-start KRT.