Background: Thyroid autoimmunity is a potentially critical factor that is often neglected in the association be-tween subclinical hypothyroidism (SCH) and depressive disorders. This study aimed to investigate the clinical correlates of autoimmune thyroiditis (AIT) and non-autoimmune hypothyroidism (NAIH) in treatment-naive patients with major depressive disorder (MDD). Method: Using a cross-sectional design, we recruited a total of 1718 outpatients with treatment-naive MDD. Demographic and relevant clinical information including duration of MDD, severity of depression and anxiety, psychotic symptoms, suicide attempts, thyroid function parameters, etc. were collected. According to thyroid function parameters, patients were classified as AIT, NAIH, latent Hashimoto's thyroiditis (LH) and euthyroidism (ET). Results: Patients with SCH (including AIT and NAIH) had older age at onset, and were more likely to have psychotic symptoms compared to those with ET. Multiple linear regression analysis showed that SCH was associated with duration of MDD and HAMD scores. Logistic regression analysis showed that the odds of having more severe anxiety and metabolic syndrome were greater among patients with SCH compared to those with ET. The odds of having suicide attempts were greater among patients with AIT than among those with ET. Limitation: Because of the cross-sectional design of this study, we were unable to sort out causality between MDD and SCH. Conclusion: Our findings suggested that AIT and NAIH were associated with duration of MDD, HAMD scores, severity of anxiety, and metabolic syndrome. However, only AIT in SCH was associated with suicide attempts.