Objective: Previous research on the implications of diabetes and dementia has shown conflicting results. In this study we report the level of impairment in executive functioning in a group of elderly individuals with comorbid Alzheimer's disease (AD) and Diabetes Mellitus (DM) as compared to three control groups. Method: Individuals who received neuropsychological testing were identified through a search of electronic medical records at a memory disorder clinic in Florida. Those who had comorbid diagnoses of AD and DM (n = 44) were compared to individuals with AD without DM (n = 44), no AD with DM (n = 52), and no AD without DM (n = 35). Mean age was 79.4 (SD = 5.69). For each subject, scores on four tests of executive functioning were discussed by a case review team to label their level of executive functioning accordingly (impaired, borderline, average). Levels of executive functioning of the four groups were compared. Results: Using a chi square test, results indicate the AD with DM group was more likely to have impaired functioning (z = 2.6, p < .001). Additionally, the no-AD no-DM group was more likely to have average functioning (z = 2.2, p < .001). There were no differences for the AD without DM and DM without AD groups. Conclusion(s): Individuals diagnosed with both AD and DM are more likely to exhibit impaired executive functioning and less likely to have average executive functioning, as compared to those without either diagnosis. These findings support previous studies that reported an increased risk of executive dysfunction in comorbid AD and DM.