Platelet endothelial cell adhesion molecule-1 (PECAM-1) has been implicated in angiogenesis through its involvement in endothelial cell-cell and cell-matrix interactions and signal transduction. Recent studies indicate that the cytoplasmic domain of PECAM-1 plays an important role in its cell adhesive and signaling properties. However, the role PECAM-1 isoforms play during angiogenic events such as cell adhesion and migration requires further delineation. To gain insight into the role PECAM-1 plays during vascular development and angiogenesis, we examined the expression pattern of PECAM-1 isoforms during kidney vascularization. We show that multiple isoforms of PECAM-1 are expressed during renal vascular development with different frequencies. The PECAM-1 that lacks exons 14 and 15 (Delta14&15) was the predominant isoform detected in the renal vasculature. To further study PECAM-1 isoform-specific functions we isolated kidney endothelial cells (EC) from wild-type and PECAM-1-deficient (PECAM-1-/-) mice with B(4)-lectin-coated magnetic beads. PECAM-1-/- kidney EC showed reduced migration, inability to undergo capillary morphogenesis in Matrigel, dense peripheral focal adhesions, and peripheral cortical actin distribution compared with wild-type cells. PECAM-1-/- kidney EC secreted increased amounts of fibronectin and decreased amounts of tenascin-C and thrombospondin-1. Reexpression of Delta14&15, but not full-length, PECAM-1 in PECAM-1-/- kidney EC restored cell migration and capillary morphogenesis defects. Thus PECAM-1 may regulate the adhesive and migratory properties of kidney EC in an isoform-specific fashion through modulation of integrin activity and extracellular matrix protein expression. Our results indicate that regulated expression of specific PECAM-1 isoforms may enable EC to accommodate the different stages of angiogenesis.