BACKGROUND: There have been few clinical studies on 10 mg atorvastatin as a starting dosage for treatment of hypercholesterolemia in type 2 diabetes mellitus (T2DM) patients. This retrospective study aims to evaluate the efficacy of 10 mg dosage of atorvastatin in clinical setting. METHODS: One hundred five enrolled patients with high levels of low density lipoprotein cholesterol (LDL-C, > 100 mg/dL) took 10 mg atorvastatin. After 6 months, they were divided into 'Responder group' (LDL-C < 100 mg/dL) and 'Non-responder group' (LDL-C > or = 100 mg/dL), and the response rate was calculated. Thereafter, we subdivided the 'Responder group' into Maintenance (10 mg), Reduced dosage (5 mg), and Discontinuance group (0 mg). The 'Non-Responder group' was subdivided into Maintenance (10 mg) and Double dosage group (20 mg). After consecutive 6 months, the response rates of each 10 mg Maintenance groups were compared to those of the other groups, respectively. RESULTS: Following the first 6 months, the response rate of 10 mg fixed dosage was 74.3%. In the 'Responder group', response rates of 10 mg, 5 mg and Discontinuance groups following 6 months were 52.6%, 53.1%, and 12.5%, respectively. In the 'Non-responder group', response rates of 10 mg and 20 mg groups were 28.6% and 50.0%. Baseline LDL-C levels and body mass index (BMI) of 'Responder group' were significantly lower than those of 'Non-responder group' (P = 0.004, respectively). CONCLUSION: Hypercholesterolemia treatment with 10 mg, fixed dosage of atorvastatin was effective in three quarters of the subjects during the first 6-month treatment; however, a significant number of patients with high LDL-C levels and/or BMI require higher starting and maintenance dosage.