Background: Cross-sectional studies find an elevated prevalence of depression among subjects with diabetes mellitus (DM). The causal mechanisms and temporal sequence of this association have not been clearly delineated. This study investigated the prospective relationship between DM and depressive symptoms. Methods: The Health, Aging, and Body Composition Study was a cohort study conducted in the metropolitan areas of Memphis, Tenn, and Pittsburgh, Pa. The analysis included 2522 community-dwelling subjects, aged 70 to 79 years, without baseline depressive symptoms. Incident depressed mood was defined as use of antidepressants at follow-up visits or presence of depressive symptoms (score ≥10 on the 10-item Center for Epidemiological Studies Depression scale). Presence of incident depressed mood at 2 consecutive annual clinic visits defined the incidence of recurrent depressed mood. Diabetes mellitus status, glycosylated hemoglobin (HbA1c) level, and DM-related comorbidities were assessed at baseline. Diabetes mellitus status was further characterized as absent, controlled (HbA1c level <7%), or uncontrolled (HbA1c level ≥7%). Discrete time survival analysis was used to estimate depressive events risk. Results: During a mean follow-up of 5.9 years, participants with DM had a higher age-, sex-, race-, and siteadjusted incidence of depressed mood (23.5% vs 19.0%) (P=.02) and recurrent depressed mood (8.8% vs 4.3%) (P<.001) than those without DM. Diabetes mellitus was associated with a 30% increased risk of incident depressed mood (odds ratio [OR], 1.31; 95% confidence interval [CI], 1.07-1.61), which was attenuated after adjustment for DM-related comorbidities (OR, 1.20; CI, 0.97-1.48). A stronger relationship was observed between DM and recurrent depressed mood (OR, 1.91; CI, 1.32-2.76), particularly among participants with poor glycemic control. Conclusion: Among well-functioning older adults, DM is associated with increased risk of depressive symptoms.