Platelet-derived growth factor (PDGF) is a critical regulator of mesenchymal cell migration and proliferation. The vital functions of PDGFs for angiogenesis, as well as development of kidney, brain, cardiovascular system and pulmonary alveoli during embryogenesis, have been well demonstrated by gene knock-out approaches. Clinical studies reveal that aberrant expression of PDGF and its receptor is often associated with a variety of disorders including atherosclerosis, fibroproliferative diseases of lungs, kidneys and joints, and neoplasia. PDGF contributes to cancer development and progression by both autocrine and paracrine signaling mechanisms. In this review article, important features of the PDGF isoforms and their cell surface receptor subunits are discussed, with regards to signal transduction, PDGF-isoform specific cellular responses, and involvement in angiogensis, and tumorstromal interactions.