Protocadherin-1 (Pcdh1) is a member of the δ-protocadherin subgroup of non-clustered protocadherins. We studied the expression of Pcdh1 from the early embryonic to the adult stage of mouse development by semi-quantitative RT-PCR and in situ hybridization. Pcdh1 can be detected as early as embryonic day 9.5. In early embryogenesis, expression is especially prominent in blood vessels. During later development and in the adult mouse, organs derived from the embryonic gut, such as the esophagus, intestines, liver, lung, and submandibular gland, contain epithelia and other types of tissues that are Pcdh1-positive. Other positive organs include the brain, spinal cord, retina, peripheral ganglia, the inner ear, hair follicles, kidney, vagina, uterus, placenta, testis, prostate, and the seminal gland. The tight spatial and temporal regulation of Pcdh1 expression suggests that this protocadherin plays multiple roles not only during development but also in mature tissues and organs in the mouse. Developmental Dynamics 237:2496–2505, 2008. © 2008 Wiley-Liss, Inc.