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Introduction: The pattern of atherosclerotic diabetic vascular disease in the lower extremities typically involves occlusive disease of the infrageniculate arteries. Accelerated proliferation and migration of arterial smooth muscle cells (ASMCs) occurs as an early event in atherosclerotic plaque formation particularly in patients with type II diabetes. The purpose of this study is to examine the effects of cilostazol, a substance that improves claudication distance in patients with lower extremity atherosclerosis, on the insulin-induced proliferation and migration of human infragenicular ASMCs harvested from diabetic patients. Methods: Human infragenicular ASMCs isolated from the tibial arteries of male diabetics undergoing lower extremity amputation were harvested and grown to subconfluence. This was followed by exposure to deprived media with and without insulin at 100 ng/ml and cilostazol (5 μM and 10 μM). Cellular proliferation was assayed at 24 hours using [methyl-3H]-thymidine incorporation. Migration assays were performed using a modified Boyden chamber. Cell viability was assessed by trypan blue assay. Results: ASMCs exposed to insulin had a significantly increased rise in thymidine incorporation (P < 0.05). When both the control (deprived media alone) and insulin groups were exposed to cilostazol (10 μM), there was a significant decrease in thymidine incorporation (P < 0.05). In the migration assay, insulin induced a significant increase (P < 0.05) in the mean number of cells per high-powered field compared to control. The addition of cilostazol (5 μM and 10 μM) resulted in a significant decrease (P < 0.05) in cell migration in all groups. Viability was not significantly different between control group, the group receiving cilostazol, and the group exposed to drug vehicle (DMSO). Conclusions: Cilostazol significantly reduces the rate of cell proliferation and migration in human diabetic ASMCs exposed to elevated concentrations of insulin without affecting cell viability. Therefore, cilostazol may have an even broader effect on ASMCs that will assist in the prevention of atherosclerotic lesion development. This may be particularly true for the type II diabetic patient. [Copyright &y& Elsevier]