OBJECTIVES:  Lifestyle diseases like diabetes are reported to be often comorbid with depression, and the symptoms of the diseases are possible to be affected. We examined the comorbidity of depression and type 2 diabetes in each patient group based on claims database analysis. METHODS:  A claims database consisted of claims data provided by Japanese health insurance societies for employees and their family members. The insured having annual health checkup data was used. Patients with type 2 diabetes and depression were extracted according to ICD-10 codes. We made a comparison of incidence of depression between type 2 diabetes patients and non-diabetic individuals, and that of type 2 diabetes between depression patients and non-depression individuals. Propensity score matching technique was applied to adjust the attributes in each cohort to minimize selection bias with the following background variables: age, sex, BMI, smoking, alcohol intake, sleep conditions, exercise habit, and physical activity. Multiple logistic regression analysis of the association of depression prevalence with these variables was conducted for type 2 diabetes patients aged ≤60. RESULTS:  We extracted 675,660 individuals having all the background variables used for propensity score matching from the database in 2014. Among them, there were 74,255 patients with type 2 diabetes patients and 21,620 patients with depression. Odds ratio of depression in type 2 diabetes patients to the others was 3.5 [90% confidence interval (CI), 2.8 to 3.9], and that of type 2 diabetes in depression patients to the others was 2.8 [90% CI, 2.4 to 3.5]. The depression prevalence in type 2 diabetes patients associated with age, alcohol intake, and sleep conditions. CONCLUSIONS:  We found a significant association between type 2 diabetes and depression, and association of depression with some factors in diabetes patients. More detailed analyses should be conducted to understand the link of these diseases.