Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) are postulated to act as endocrine disrupters. In the ongoing Duisburg birth cohort study, started in 2000-2002, influence of persistent organic pollutants (POP) on child development was monitored. For the first time, associations were reported between prenatal and postnatal PCDD/F and PCB exposures and early endocrinological changes concerning adrenarchal development. PCDD/F and PCB concentrations were measured in blood samples taken in wk 32 of pregnancy and in breast milk using gas chromatography and high-resolution mass spectrometry (GC/HRMS). At the age of 6-7 and 8-9 yr, serum samples were collected from 111 children. The samples were assayed for the sex hormones testosterone, estradiol, dehydroepiandrosterone sulfate (DHEA-S), and 17-OH-progesterone (17-OHP) by using an automated chemiluminescence assay system. Analyses of repeated measurements of DHEA-S serum levels were performed by linear regression analysis using generalized estimating equations (GEE). Linear regression analysis showed a positive association between DHEA-S and breast milk levels of PCDD/F and PCB expressed as toxicity equivalents according to toxicity equivalent factors published by the World Health Organization (WHO) in 2005 (WHO(2005)-TEq) (increase of 29%, geometric mean ratio, GMR: 1.29, 95% CI 1.06-1. 58 per doubling of PCDD/F + PCB WHO(2005)-TEq levels). Results for the association with the WHO(2005)-TEq levels in blood of mothers were in the same direction (increase of 15%, GMR 1.15, 95% CI 0.93-1.42 per doubling of PCDD/F + PCB WHO(2005)-TEq levels), but not significant. Data indicate that PCDD/F and PCB exposure in infancy may influence DHEA-S serum levels in prepubertal children. Increased DHEA-S serum levels are considered to indicate acceleration of the adrenal maturation.