Vitamin D3 is a fatsoluble secosteroid hormone, which is synthesized in the skin (under the influence of ultraviolet light from the sun) or obtained from food. Metabolites of vitamin D3, 25hydroxyvitamin D3 (25(OH)D) and 1alpha,25dihydroxyvitamin D3 (1,25(OH)2D), have their effects through the vitamin D receptor (VDR), and alter the expression of specific target genes. The vitamin D3 endocrine system is essential for calcium and bone homeostasis. Many brain cells, several regions of the central nervous system and muscle cells express VDRs. The central nervous system is increasingly recognized as a target organ for vitamin D3. Several clinical and experimental/animal data show regulation of physiological brain functions (such as neuroprotection, antiepileptic effects, immunomodulation, regulation of behavior, as well as motor functions) by vitamin D. The present study was focused on the biological action of the vitamin D/VDR system in adult nervous system, as revealed by studying animals with genetically modified VDR, or genes involved in vitamin D metabolism. VDR knockout mice develop abnormal emotional behaviors, such as neophobia, and increased seizures following pentylenetetrazole administration. 1,25(OH)2D also regulates seizure activity in two wild type mouse strains. VDR mutant mice displayed impaired hearing and balance functions. Also, developed swimming impairments. The gustatory and olfactory functions, spatial memory, and hedonic response of VDR deficient mice were unimpaired. Collectively, the present study demonstrates that vitamin D regulates various functions of the nervous system, confirming that the brain could be considered as a target organ for vitamin D.