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].Being intrigued by Dr. Koo's suggestion regarding age-group-specific projections, further analysis has been attempted; projected prevalence estimates are 10.6% (7.8% in women and 13.4% in men) for adults aged 20 to 64 years (the younger) and 43.6% (31.7% in women and 55.4% in men) for those aged 65 to 79 years (the older) when considering the population projection at 2030 [6]. Before considering it, however, 9.1% (6.3% in women and 11.9% in men) in the younger and 26.8% (23.1% in women and 30.4% in men) in the older have been estimated. Interpreting these results, I agree with Dr. Koo's speculation regarding an increasing trend in DM prevalence among male adults due to increasing prevalence of risk factors including obesity as well as among male and female elders due to an increasing size of the elderly population. Thus, the suggestion of forecasting age-specific prevalence of DM is quite worthy of being considered.