Objectives To determine the effect of beta(3)-adrenergic receptor (AR) agonist on the risk of kidney cancer in patients with overactive bladder (OAB). Patients and methods A nationwide population cohort study was conducted using data from the Korean National Health Insurance System database between January 2016 and December 2023. Validation analyses were performed using clinical data from patients with OAB treated with mirabegron or anticholinergics at a tertiary referral hospital between January 2014 and December 2023. The main exposure was intake of beta(3)-AR agonist or anticholinergics, and the main outcome was incidence of kidney cancer. Results Of the 1 419 148 patients (61.6% male; median [interquartile range] age, 64 [53-73] years), 3229 developed kidney cancer after OAB treatment. The incidence rate of kidney cancer was 0.7 per 1000 person-years in the mirabegron group and 0.5 per 1000 person-years in the anticholinergic group. Among the validation data of 3108 patients (49.3% male; mean [standard deviation] age, 63.9 [13.3] years), 45 (1.4%) developed kidney cancer after OAB treatment. The mirabegron group had a higher incidence of kidney cancer (1.8%) than the anticholinergic group (0.7%) (P = 0.025). Conclusions Use of beta(3)-AR agonists was associated with an increased risk of kidney cancer compared with anticholinergics. While these findings suggest a potential association between mirabegron use and kidney cancer, further studies are needed to confirm causality. Clinicians should exercise caution when prescribing mirabegron in patients with risk factors for kidney cancer.