The choroid plexus epithelium (CPe) is a specialized epithelium involved primarily in the production of cerebrospoinal fluid (CSF) which is important for maintaining an optimal homeostatic environment for the brain. Although, the physiology of the CPe is fairly well understood, its development has not been thoroughly studied. It has been recently shown that mice lacking functional transcription factors, E2F5, foxJ1 or p73, develop non-obstructive hydrocephalus likely due to CPe dysfunction. We have further studied their expression in the mouse and human developing CPe, focusing particularly on E2F5. We show here that in the mouse E2F5, foxJ1 and p73 transcripts are detectable as soon as the choroid plexuses form. E2F5 protein is also detected as soon as the choroid plexuses are morphologically apparent both in mouse and human, suggesting that its expression is regulated at the transcriptional level. E2F5 protein is down-regulated late in embryogenesis and this coincides with a change in its intracellular localization, from predominantly nuclear to cytoplasmic. The pattern of expression and intracellular localization of E2F5 in vivo does not appear to correlate with that of proliferating CPe cells, as indicated by protein cell nuclear antigen (PCNA) staining, but rather with their maturation, as changes in E2F5 localization from the nucleus to the cytoplasm parallel the morphological change from pseudostratified to cuboidal epithelium.