To compare the strength of the association between depression and mortality between elderly and younger individuals with diabetes mellitus. A survival analysis conducted in a longitudinal cohort study of persons with diabetes mellitus to test the association between depression and mortality in older (? 65) and younger (18-65) adults. Managed care. Persons aged 18 and older with diabetes mellitus who participated in the Wave 2 survey of the Translating Research Into Action for Diabetes (TRIAD) Study (N = 3,341). The primary outcome was mortality risk, which was measured as days until death using linked data from the National Death Index. Depression was measured using the Patient Health Questionnaire. After controlling for age, sex, race and ethnicity, income, and other comorbidities, mortality risk in persons with diabetes mellitus was 49% higher in those with depression than in those without, although results varied according to age. After controlling for the same variables, mortality risk in persons aged 65 and older with depression was 78% greater than in those without. For those younger than 65, the effect of depression on mortality was smaller and not statistically significant. This analysis suggests that the effect of depression on mortality in persons with diabetes mellitus is most significant for older adults. Because there is evidence in the literature that treatment of depression in elderly adults can lead to lower mortality, these results may suggest that older adults with diabetes mellitus should be considered a high-priority population for depression screening and treatment.