Circulating progenitor cells (CPCs) and endothelial progenitor cells (EPCs) are immature cells involved in vascular repair and related to many aspects of cardiovascular and microvascular diseases. Although there is some uncertainty in the definition of CPC and EPC and in their potential role in vascular biology, these circulating cells are being used as cellular biomarkers in several clinical settings. This presentation highlights how a reduced level of circulating progenitor cells is a risk factor for the development of future cardiovascular events and death. In addition, low CPCs/EPCs levels predict the onset or worsening of microalbuminuria and retinopathy in diabetic patients.