Despite a growing body of evidence that Vitamin D is involved in mammalian brain functioning, there has been a lack of direct evidence about its role in the human brain. This paper reports, for the first time, the distribution of the 1,25-dihydroxyvitamin D3 receptor (VDR), and 1a-hydroxylase (1a-OHase), the enzyme responsible for the formation of the active vitamin in the human brain. The receptor and the enzyme were found in both neurons and glial cells in a regional and layer-specific pattern. The VDR was restricted to the nucleus whilst 1a-OHase was distributed throughout the cytoplasm. The distribution of the VDR in human brain was strikingly similar to that reported in rodents. Many regions contained equivalent amounts of both the VDR and 1a-OHase, however the macrocellular cells within the nucleus basalis of Meynert (NBM) and the Purkinje cells in the cerebellum expressed 1a-OHase in the absence of VDR. The strongest immunohistochemical staining for both the receptor and enzyme was in the hypothalamus and in the large (presumably dopaminergic) neurons within the substantia nigra. The observed distribution of the VDR is consistent with the proposal that Vitamin D operates in a similar fashion to the known neurosteroids. The widespread distribution of 1a-OHase and the VDR suggests that Vitamin D may have autocrine/paracrine properties in the human brain.