Abstract: AIM:To investigate the effects of simvastatin on the levels of peripheral blood leukocyte count, serum total cholesterol and triglycerides in patients with diabetes mellitus and impaired fasting glucose/impaired glucose tolerance (IFG/IGT). METHODS: Diabetes mellitus patients ［n=57, 48 males, average age (74±9) years］, IFG/IGT patients ［n=42, 35 males, average age (73±6) years］ and controls ［n=44, 37 males, average age (74±7) years］ were subjected to simvastatin treatment (20 mg/day) for 6 months. Patients in all three groups performed normal physical activity and plasma samples were collected after overnight fasting at baseline before and after the 6-month treatment for examination. RESULTS: Simvastatin treatment significantly reduced the peripheral blood leukocyte count and percentage of neutrophils in IFG/IGT and patients with diabetes mellitus (P<0.01, P<0.05). Post-treatment levels of plasma triglycerides were significantly lower than those pre-treatment in patients with diabetes mellitus and IFG/IGT (P<0.01). Post-treatment levels of total plasma cholesterol were significantly lower compared with those pre-treatment in all three groups (P<0.01, P<0.05). CONCLUSION: Simvastatin markedly lowered peripheral blood leukocyte count and plasma triglyceride levels and the percentage of neutrophils in patients with diabetes mellitus and IFG/IGT. Statin-induced inhibition of peripheral blood leukocyte count may play an important role in the pharmacological treatment of cardiovascular diseases.