This is to study the incidence of Diabetes and its risk factors in the impaired glucose tolerence group. 1084 subjects who had been examined 3 times for regular check-up in one human dock center under the university hospital were studied between $1986{sim}1993$. The results are as follows; Prevalence rate of diabetes was 3.56%, and that of impaired glucose tolerence was 30.90% as of initial examination. The rate of diabetes was increasing with the age where 1.2% at age group $30{sim}39$, 3.21% at age group $40{sim}49$, 5.84% at age group $50{sim}59$, 14.28% at age group 60 and over. And also the rate of impaired glucose tolerance was increasing with the age where 21.29% at age group $30{sim}39$, 31.42% at age group $40{sim}49$, 38.91% at age group $50{sim}59$, 33.33% at age group 60 and over Of the examinees who were initially examined, total incidence rate of diabetes who developed to obvious diabetes at the 3rd follow-up examination from the initially impaired glucose tolerence group was 4.63% and it was 11.3 times higher than from the normal group (0.41%). After controlling for the effects of both age and obesity, the risk of subsequent diabetes for subjects with impaired glucose tolerance remained significantly higher than for normal subjects (Relative Risk, 10.48). Test for trends for developing to diabetes by the increasing level of fasting blood sugar and 1hr blood sugar at the initial examination were statistically significant in either normal and impaired glucose tolerence group. To determine the risk factor for developing to diabetes, logistic regression test was applied. Only fasting blood sugar and 1hr blood sugar were predictors for developing diabetes from the impaired glucose tolerence group at initial examination.