The casein kinase-1 (Ck1) family are serine/threonine specific protein kinases. They are highly associated with Alzheimer disease (AD) brain-derived tau filaments and granulovacuolar bodies. Recently we have demonstrated that one family member, Ckidelta, colocalizes with tau containing neurofibrillary tangles (NFTs) and other tau deposits in a number of neurodegenerative diseases. Here we show that the association in AD is accompanied by a sharp upregulation of Ckidelta mRNA in brain but not in peripheral organs. The degree of upregulation in AD brain is correlated with the degree of regional pathology. There was a 24.4-fold increase of Ckidelta mRNA in AD hippocampus compared with control, 8.04-fold in the amygdala, 7.45 in the entorhinal cortex and 7.30-fold in the midtemporal gyrus. These are areas with a high burden of NFTs, neuropil threads and dystrophic neurites. In areas almost devoid of this tau pathology, such as the caudate nucleus, occipital cortex and cerebellum, the increases in AD compared to control brain were only 2.21-, 1.89- and 1.87-fold, respectively. Western blot analysis showed that the upregulation of Ckidelta mRNA was paralleled by an upregulation of Ckidelta protein. These data establish that the association of Ckidelta with the tau pathology of AD is reflective of an increase in gene transcription. Since Alzheimer-like phosphoepitopes of tau can be generated by Ck1, the Ckidelta isoform may play an important role in this fundamental aspect of AD pathology.