Objective To evaluate the therapeutic efficiency and safety of metformin in non-obese elderly patients with type 2 diabetes mellitus(T2DM).Methods A total of 228 elderly T2DM patients admitted in Chinese PLA General Hospital between January 1996 and September 2006 were analyzed retrospectively.The changes in fasting blood glucose(FBG),post blood glucose(PBG),HbA1c,blood lipid level,liver and kidney function,blood lactic acid and body mass before and after metformin administration were compared between obese and non-obese patients.Results The levels of FBG,PBG,HbA1c,total cholesterol(TC),and low density lipoprotein cholesterol(LDL-C) in both obese and non-obese patients were all significantly reduced after metformin treatment(P<0.01),but with no difference between the two groups.Body mass,body mass index(BMI),and the level of triglycerides(TG)were significantly reduced after metformin treatment in both groups,more significantly in obese group than in non-obese group(P<0.01).The liver and kidney function had no significant change after treatment.No lactic acidosis was reported.Conclusion Metformin treatment is effective and safe in both obese and non-obese elderly T2MD patients.