The number of diabetic patients has been increasing in Japan and consequently diabetic complications are the most important target to be prevented through improving glycemic control. In order to describe the glycemic control status and treatment of diabetic patients by specialists in Japan over three years, from 2000 to 2002, we examined HbA1c, other laboratory data and the modality of drug therapy in the study population, 8170 in 2000, 11,831 in 2001, and 16,934 in 2002. Patients were registered at clinics and hospitals that were members of the Japan Diabetes Clinical Data Management Study Group (JDDM). HbA1c levels, other laboratory data, and details of drug therapy were collected and analyzed using SPSS and MS Access. The mean HbA1c levels were essentially unchanged during the study periods, ranging from 7.9% to 7.8%, and from 7.1% to 7.0%, in type 1 and type 2 diabetic patients, respectively. In type 2 diabetes, the frequency of oral hypoglycemic agents (OHA) use increased from 44.9% to 51.4%, while the use of diet-only therapy decreased from 29.9% to 25.4% over the study period. Although the systolic blood pressure was slightly above target, the mean blood pressure and the mean lipid profile were mostly within the treatment goals set by the Japan Diabetes Society. This first report from a large scale study of the daily management of diabetes in Japan revealed that the average HbA1c level was superior to most of the results reported from other countries. Nonetheless, 66% of the patients still had HbA1c levels and half of the patients had other laboratory parameters including blood pressure and lipid profile that were greater than those recommended by the Japan Diabetes Society. The nature of diabetes drug therapy in Japan has gradually changed as new drugs have appeared in the market.