Diabetes is one of the major noncommunicable diseases found worldwide. Different researchers have reported the predicted and observed prevalence of diabetes and the number of people with diabetes over different years in China and in other countries. This review provides a new insight into the growing epidemic of diabetes in recent decades and in the coming future by comparing projected and observed prevailing trends of this disease reported in the international literature. The review found that the projected burden of diabetes for China in each time point from 2000 to 2030 underestimated the epidemic of diabetes in terms of the prevalence and the total number of people with the disease. Based on a recent Chinese national survey, the observed prevalence and the total number of people with diabetes in 2008 (9.7% and 92.4 million, respectively) were remarkably higher than that expected for 2009 or 2010 (3.9% and 53.1 million for 2009, and 4.5% and 43.2 million for 2010). The observed 2008 figures were even much higher than the projected prevalence and the number of people with diabetes for 2030. The tendency to underestimate future diabetes epidemics also occurs in many other countries, especially those characterized by low and middle incomes.