['Depression is not adequately diagnosed in many cases. Therefore, the question arises as to whether markers exist for depression. We investigated whether the presence of thyroperoxidase antibodies (TPOAbs) during pregnancy can be regarded as a marker for depression in the first year postpartum, particularly in relation to (overt or subclinical) thyroid dysfunction and other determinants of depression.', 'This work was a prospective observational study.', 'A cohort of 310 unselected women (residing in the Kempen Region, southeastern Netherlands) were visited at 12 and 32 weeks gestation and at 4, 12, 20, 28 and 36 weeks postpartum.', 'At each visit, TSH, free thyroxine and TPOAb testing was performed, determinants associated with depression were asked for, and depression was assessed (according to the Research Diagnostic Criteria). Multiple logistic regression was performed to determine independent risk factors (odds ratios, ORs) for depression in gestation and/or postpartum depression.', 'Data for 291 women were available for analysis; 41 women (14.1%) had TPOAbs at one or more time points, and 117 women (40.1%) had depression at one or more time points postpartum. The multiple logistic regression analysis showed that TPOAbs were independently associated with depression at 12 weeks gestation and at 4 and 12 weeks postpartum (OR, 95% confidence interval: 2.4 (1.1-6.0), 3.8 (1.3-7.3) and 3.6 (1.2-7.1) respectively). After the exclusion of women who were depressed at 12 weeks gestation (n=70), the presence of TPOAbs during early pregnancy was still found to be associated with the development of postpartum depression (OR, 95% confidence interval: 2.8 (1.7-4.5); after exclusion of women who had had depression in earlier life (n=51), TPOAb during early gestation was still associated with postpartum depression (OR, 95% confidence interval: 2.9 (1.8-4.3).'] Are thyroid peroxidase antibodies during gestation a marker for subsequent depression postpartum?