Diabetes mellitus (DM) increases the risk of cardiovascular disease and is associated with sudden death. Mental illness among individuals with DM may confound medical care. This study assessed the association of mental illness with DM and poorly controlled DM in sudden death victims. We screened out-of-hospital deaths ages 18 to 64 years in Wake County, North Carolina from 2013 to 2015 to adjudicate sudden deaths. We abstracted demographics and clinical characteristics from health records. Mental illness included anxiety, schizophrenia, bipolar disorder, or depression. Poorly controlled DM was defined as a hemoglobin A1c >8 or taking ≥3 medications for glycemic control. Logistic regression assessed the association between DM and mental illness. Among victims with available records, 109 (29.4%) had DM. Of those, 62 (56.9%) had mental illness. Mental illness was present in 53.42% and 63.89% of victims with mild and poorly controlled DM, respectively. Mental illness was associated with DM (adjusted odds ratio 2.46, 95% confidence interval 1.57-3.91). Victims with poorly controlled DM were more likely to have mental illness (adjusted odds ratio 2.66, 95% confidence interval 1.14-6.18). DM is a common comorbid condition in sudden death victims. Among victims, mental illness is associated with the control of DM. Early management of comorbid mental illnesses may improve the care of patients with DM and reduce the incidence of sudden death.