I would like to express my sincere thanks for Dr. Koo's comments on the recently published article about the projected prevalence of diabetes mellitus (DM) in Korean adults [1]. In this article, the current and future prevalence estimates of DM were calculated among adults aged 30 years or older because this age-range was used in the report of the Korea National Health and Nutrition Examination Survey [2]. Accordingly, it is reasonable that the projected prevalence for the year 2030 presented in the article [1] was relatively higher than an estimate among adults aged 20 to 79 years proposed by the International Diabetes Federation (IDF) [3]. In addition, the method which was used to obtain the IDF's estimates is likely to produce underestimated projections as indicated in an earlier report [4]. If the denominator is changed into the number of adults aged 20 to 79 years, the prevalence of DM at the year 2030 would be 18.9% (13.8% in women and 23.9% in men) using the same method of the article [1]. Furthermore, if the denominator is the number of the total Korean population, the prevalence of DM at the year 2030 would be 14.2% (10.0% in women and 18.3% in men), which is comparable to the prevalence (15.3%) projected in the total United States population [5]. The IDF has also speculated that the projections of DM prevalence for the United States and Republic of Korea at the year 2030 would be similar [3].