Aims: The aim of this phase 1 trial was to assess the pharmacokinetics, safety, and tolerability of balcinrenone (previously AZD9977) in participants with severe renal impairment versus those with normal renal function. Methods: Participants with severe renal impairment (estimated glomerular filtration rate [eGFR] <30 mL/min/1.73 m2) not on dialysis were compared with group-matched control participants with eGFR ≥90 mL/min/1.73 m2. Eligible participants received a single oral dose of 150 mg balcinrenone, and blood and urine samples were collected for analysis. Results: The total apparent balcinrenone clearance was 50% lower in the severe renal impairment group, resulting in a ~two-fold higher area under the curve (AUC) and a 1.4-fold higher maximum observed plasma concentration in the severe renal impairment group versus the control group. The terminal half-life and plasma protein binding were similar in both groups. Balcinrenone was safe and well tolerated in all participants. All adverse events reported were of mild-to-moderate severity and not considered related to balcinrenone. Conclusions: Balcinrenone exposure was approximately two-fold higher in participants with severe renal impairment compared with the group-matched control participants. Based on obtained results, the AUC exposure is predicted to be <50% higher in patients with an eGFR of 20 mL/min/1.73 m2 compared with those with an eGFR of 60 mL/min/1.73 m2. In light of these findings, no dose adjustment based on eGFR is needed in two ongoing studies that target these patients (MIRO-CKD [NCT06350123] and BalanceD-HF [NCT06307652]).