A large number of children with type 2 diabetes have been detected by a urine glucose screening program conducted at schools in Japan since 1975. The incidence of type 2 diabetes in children has increased over the last three decades, and the incidence is estimated to be approximately 3.0/100,000/y during 1975-2000. The incidence of type 2 diabetes in junior high school children is three to six times higher than that in primary school children. More than 80% of children with type 2 diabetes are obese, and boys are more likely to be obese than girls. It is speculated that the increase in the incidence of childhood type 2 diabetes over the years may be a consequence of the increase in the frequency of obesity in school children. However, this trend of increasing incidence of childhood obesity has recently become weaker, and perhaps as a consequence, the incidence of type 2 diabetes has also decreased after the year 2000 in some cities of Japan. Improved attention to physical activity and eating habits among young people may be responsible at least in part to the decrease in the incidence of type 2 diabetes noted in recent years in big cities of Japan.