We assessed the prevalence of minor mental disorder and depression in elderly patients with non-insulin-dependent (Type 2) diabetes mellitus as compared with control subjects and evaluated the associates of impaired mental well-being in diabetic patients. The study consists of a community-based group of patients (n = 82) with a 10 years' known duration of disease and nondiabetic control subjects (n = 115). In addition to clinical and laboratory examinations, self-rating questionnaires assessing minor mental disorder (General Health Questionnaire, GHQ) and depression (Zung Self-rating Depression scale) were completed by the patients and control subjects. The mean scores of GHQ and Zung scores tended to be higher in diabetic than in control subjects, but the frequency of case subjects was not different between the diabetic (GHQ: 40%; Zung: 11%) and nondiabetic groups (GHQ: 36%; Zung: 7%). These findings were explained by more severe symptoms in diabetic case subjects as compared to nondiabetic case-subjects. From the various parameters studied, the presence of symptomatic neuropathy was most strongly associated with depression and minor mental disorder in diabetic subjects. The results suggest that the impact of Type 2 diabetes per se on minor mental disorder or depression in elderly subjects is not overwhelming. However, a subgroup of diabetic patients seems to have markedly impaired mental well-being, and the treatment of its underlying factors may improve overall treatment compliance.