The Notch family of receptors and downstream effectors plays a critical role in cell fate determination during vascular ontogeny. Moreover, the human cerebral autosomal dominant artriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) syndrome of premature stroke and dementia is a heritable arteriopathy with alterations in vascular smooth muscle cells (VSMCs) resulting from mutations within Notch3. However, the expression and regulation of the Notch and hairy-related transcription factor (HRT) pathway in adult VSMCs in vitro and in vivo remain poorly characterized. The present study documents that the well-described modulation of VSMC fate in response to vascular injury and growth factor activation involves a coordinate regulation of the Notch and HRT pathways. Furthermore, platelet-derived growth factor promotes a similar coordinate down-regulation of the Notch receptors and HRT genes in cultured VSMCs via an ERK-dependent signaling pathway. Moreover, we established that HRT1 and HRT2 are direct downstream target genes of Notch3 signaling in VSMCs and determined that the activity of the nuclear protein RBP-Jk is essential for their regulation. These findings provide initial insight into the context- and cell type-dependent coordinate regulation of Notch3 and downstream HRT transcriptional pathway effector genes in VSMCs in vitro and in vivo that may have important implications for understanding the role of Notch signaling in human health and vascular disease.