Vascular leiomyomas are believed to arise from the smooth muscle of blood vessels and are characterized by the proliferation of vascular smooth muscle cells (VSMC) and numerous slit-like vascular lumens. Parathyroid hormone (PTH)-related peptide (PTHrP) plays an important role in local autocrine and/or paracrine regulation of cellular growth and function in VSMC. To investigate the interaction between VSMC and endothelial cells, we evaluated the distribution of PTHrP and PTH/PTHrP-receptor in 10 vascular leiomyomas of the skin by immunohistochemistry and in situ hybridization (ISH) of paraffin-embedded specimens. Both immunohistochemistry and ISH revealed that PTH/PTHrP-receptors are expressed in endothelial cells lining areas with slit-like vascular lumens and very weakly expressed in proliferating VSMC in all vascular leiomyomas. On the other hand, PTHrP itself was localized mainly in proliferating VSMC. These results support the hypothesis that PTHrP acts through the PTH/PTHrP-receptor via an autocrine and/or paracrine mechanism from VSMC to endothelial cells in the formation of characteristic microenvironments of vascular leiomyoma cell composition.