Comorbid anxiety disorders in patients with mood disorders have a negative impact on outcomes, such as persistence of depressive symptoms, deterioration of quality of life (QoL), increased suicide risk, mood instability with antidepressant treatment, but often go underrecognized in clinical practice. To identify features useful for supporting the confirmation of comorbid anxiety disorders, we investigated the prevalence of comorbid anxiety disorders and their associated factors in Japanese patients with mood disorders using data from our previously reported JET-LMBP study. Patients with bipolar disorder (BD; n=114) and patients with major depressive disorder (MDD; n=334), all with major depressive episodes (DSM-IV-TR) were analyzed. Comorbid anxiety disorders were confirmed using the Mini-International Neuropsychiatric Interview. Demographic and clinical features were assessed using patient background forms, including the Quick Inventory of Depressive Symptomatology-Self Report Japanese version, 36-Item Short-Form Health Survey (SF-36), and Child Abuse and Trauma Scale (CATS). Multivariate logistic regression analysis adjusted for age, sex, and severity of depressive symptoms was used to identify factors associated with comorbid anxiety disorders (post hoc analysis). The prevalence of comorbid anxiety disorders was significantly higher in patients with BD (53.2%) than in patients with MDD (37.2%). Factors associated with comorbid anxiety disorders in BD included no spouse, interpersonal rejection sensitivity, higher CATS sexual abuse scores, and lower SF-36 mental component summary scores. In MDD, factors included hypersomnia, pathological guilt feelings, higher CATS neglect scores, and lower SF-36 physical component summary scores. Comorbid anxiety disorders were commonly seen in Japanese patients with mood disorders. Childhood abuse, atypical depression symptoms, and deterioration of health-related QoL were commonly associated with comorbid anxiety disorders in BD and MDD, suggesting that the presence of these features may be useful to support the confirmation of comorbid anxiety disorders in these patients. © 2020 Inoue et al.