Objective: This study was conducted to compare the adherence, clinical and economical utility of fixed-dose combination tablets of sitagliptin/metformin with concomitant administration of sitagliptin and metformin in patients with type 2 diabetes mellitus. Methods: Adherence was measured as the medication possession ratio (MPR) of ${geq}80%$, and MPR was calculated as the number of total prescription days divided by the total treatment period. Hemoglobin $A_{1C}$ ($HbA_{1c}$) differences between baseline and predetermined periods were analyzed. Proportions of patients who achieved $HbA_{1c}$ less than 6.5% for three or more consecutive times were compared. To evaluate cost-effectiveness, prices of sitagliptin, metformin and sitagliptin/metformin tablets were investigated. Results: More than 90% of patients showed adherence in both groups (92.0% in fixed-dose combination group vs 95.9% in concomitant administration group), and there was no statistically significant difference (P = 0.113). Proportion of patients with HbA1c less than 6.5% for three or more consecutive times tended to be somewhat higher in fixed dose combination group than in concomitant administration group without a statistically significant difference (32.6% vs. 28.0%, P = 0.344). Total price of metformin and sitagliptin was cheaper up to 222 KRW in the case of fixed-dose combination tablets compared to the case of concomitant administration. Conclusion: The sitagliptin/metformin fixed-dose combination tablet had a similar patient adherence and was not significantly different in efficacy to the concomitant administration of each component. In terms of drug prices, fixed-dose combination tablets were cheaper than concomitant administration of each tablet.