p,p'-DDE, or ethylene, 1,1-dichloro-2,2-bis(p-chlorophenyl), is the main metabolite of the pesticide DDT, or 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane. It is an androgen receptor antagonist and testosterone hydroxylase modulator that is also more persistent than its parent compound. In a previous study we demonstrated that embryonic exposure to different doses of p,p'-DDE accelerated onset of puberty in females and reduced male reproductive behavior. In the present study we investigated the long-term effects of the exposure to p,p'-DDE on the differentiation of male Japanese quail (Coturnix japonica) limbic circuits related to male copulatory behavior: the parvocellular vasotocin (VT) system. We observed a decrease in the density of VT-immunoreactive fibers within the medial preoptic nucleus, bed nucleus of the stria terminalis, and lateral septum in p,p'-DDE-treated birds, while no differences could be detected in the magnocellular neurons of the supraoptic nucleus. In particular the lowest dose of p,p'-DDE causes the highest decrease of VT immunoreactivity. This study provides further evidence for VT system sensitivity towards endocrine disrupting chemicals and demonstrates that the VT system may be an appropriate and sensitive biomarker for early p,p'-DDE exposure in birds.