Evidence for the presence of the vitamin D receptor in brain implies this vitamin may have some function in this organ. This study investigates whether vitamin D3 acts during brain development. We demonstrate that rats born to vitamin D3-deficient mothers had profound alterations in the brain at birth. The cortex was longer but not wider, the lateral ventricles were enlarged, the cortex was proportionally thinner and there was more cell proliferation throughout the brain. There were reductions in brain content of nerve growth factor and glial cell line-derived neurotrophic factor and reduced expression of p75NTR, the low-affinity neurotrophin receptor. Our findings would suggest that low maternal vitamin D3 has important ramifications for the developing brain.