Evidence suggests that older adults with mild cognitive impairment (MCI) might not receive evidence-based treatments. We explored the impact of patient MCI on physician decision-making and recommendations for acute ischemic stroke (AIS) and acute myocardial infarction (AMI) in a pilot concurrent mixed-methods study of physicians recruited from one academic center. The mailed survey included a clinical vignette of AIS or AMI where the patient cognitive status was randomized (normal cognition, MCI, or early-stage dementia). The primary outcome was a composite summary measure of the proportion of guideline-concordant treatments recommended. Linear regression compared the primary outcome across patient cognition groups adjusting for physician characteristics. Semi-structured interviews done with 18 physicians (4 cardiologists, 9 neurologists, 5 internists) using a standard guide. Survey response rate was 72% (82/114) (49/61 neurologists; 33/53 cardiologists). As patient cognition worsened, neurologists recommended less guideline-concordant treatments after AIS (Ptrend<0.001 across patient cognition groups). Cardiologists did not after AMI (Ptrend = 0.11) in adjusted analyses. Neurologists' recommendation of guideline-concordant treatments after AIS was non-significantly lower in patients with MCI (composite measure, 0.13 points lower; P = 0.14) and significantly lower in patients with early-stage dementia (0.33 points lower; P<0.001) compared to cognitively normal patients. Interviews identified themes that may explain these findings including physicians assumed patients with MCI, compared with cognitively normal patients, have limited life expectancy, frailty and poor functioning, prefer less treatment, might adhere less to treatment, and have greater risks or burdens from treatment. These results suggest that patient MCI influences physician decision-making and recommendations for AIS and AMI treatments.