Ruboxistaurin is a potent and specific inhibitor of the beta isoform of protein kinase C. Overactivation of protein kinase C has been demonstrated in patients with type 2 diabetes, and is postulated to play a major role in the pathogenesis of diabetic microvascular complications, which include diabetic retinopathy, neuropathy and nephropathy. The role of protein kinase C in promoting tissue injury in patients with diabetes, and the pharmacologic and clinical studies illustrating the potential of ruboxistaurin to reduce the burden of diabetic microvascular complications will be discussed in this article.