OBJECTIVES: To measure the mental well-being experienced by patients with type 2 diabetes (T2D) by utilizing the SF-36v2 mental component summary (MCS). METHODS: Data were from the 2013 U.S. National Health and Wellness Survey. Respondents (aged ≥18 years) provided details about their health status and health care through self-administered, Internet-based questionnaires. The analytic sample included those self-reporting a T2D diagnosis. Mental well-being was defined by utilizing the SF-36v2 MCS. Based on the normed mean of 50 and standard deviation (SD) of 10 for the general population and the distribution of MCS scores within the analytic sample, categories were defined as good mental well-being (above the population mean; MCS ≥ 50), poor mental well-being (≤1 SD below the population mean; MCS ≥ 40 and <50), and very poor mental well-being (>1 SD below the population mean; MCS<40). RESULTS: The analytic sample consisted of 7852 respondents diagnosed with T2D.  Of these, 22% (n=1701) experienced very poor mental well-being, 23% (n=1781) poor mental well-being, and 56% (n=4370) good mental well-being.  Very poor/poor mental well-being was associated with respondents who were younger, female, non-white, less educated, current smokers, and had lower household income (p<0.001 for all).  Respondents with very poor/poor mental well-being vs. good mental well-being had greater Charlson Comorbidity Index scores (mean of 1.99/1.77 vs. 1.59), and were more likely to be diagnosed with depression (57%/26% vs. 5%) or an anxiety disorder (44%/20% vs. 5%) (p<0.001 for all).  Poorer mental well-being also was associated with having T2D for a shorter period of time, use of insulin, experience with hypoglycemia, and greater likelihood of T2D related complications (p<0.001 for all). CONCLUSIONS: Poorer mental well-being, as measured by the SF-36v2 MCS, is associated with greater overall physical and psychiatric morbidity, as well as morbidity specifically associated with T2D.