BACKGROUND: Kidney cancer is the fastest-growing cancer diagnosis in the developed world. About 16% of new cases are stage IV, which has a low five-year survival rate. Many patients with metastatic renal cell carcinoma (mRCC) are older and may have mild cognitive impairment or dementia (MCI/D). Given prior reports of patients with dementia initiating less cancer therapy and the importance of oral anticancer agents (OAAs) in mRCC treatment, we investigated the prevalence of preexisting MCI/D in patients with mRCC and their OAA use. METHODS: SEER-Medicare patients were analyzed who were ≥65 years, diagnosed with mRCC between 2007 and 2015, and had Medicare part D coverage. Patterns and predictors of (a) OAA utilization within the 12 months following mRCC diagnosis and (b) adherence (percent of days covered [PDC] ≥ 80%) during the first 90 days following treatment initiation were assessed. RESULTS: Of the 2792 eligible patients, 268 had preexisting MCI/D, and 907 initiated OAA treatment within 12 months of mRCC diagnosis. Patients with preexisting MCI/D were less likely to begin an OAA than those without MCI/D (fully-adjusted HR 0.53, 95% CI 0.38-0.76). Among OAA initiators, a preexisting MCI/D diagnosis did not alter the likelihood that a person would be adherent (adjusted RR 0.84, 95% CI 0.55-1.28). CONCLUSIONS: Patients with preexisting MCI/D were half as likely to start an OAA during the year following mRCC diagnosis than patients without comorbid MCI/D. The 90-day adherence of OAA initiators was not significantly different between those with and without preexisting MCI/D. In light of this, clinicians should assess mRCC patients for cognitive impairment and take steps to optimize OAA utilization by those with MCI/D.