Background: We first launched the case management program for diabetic patients who were registered in NHIC (National Health Insurance Corporation) in Korea and conducted this study to assess the effectiveness of the program. Methods: During the period from October in 2002 to March in 2003, 30 case managers performed the program for 71 diabetic patients. We evaluated the effectiveness of the program based on the results of fasting blood sugar level, two hour post-prandial blood sugar level, knowledge for diabetes, difficulty index in diabetes management, and the health risk factor changes of them. We analyzed results related to these factors through $x^2$ test and paired t-test. Results: The ave rage age of the subjects was 58.9. and the numbers of women and men were 43 and 28 respectively. The fasting blood sugar level and two hour post-prandial blood sugar level decreased from 164.3mg/dl to 146.5mg/dl and from 224.0mg/dl to 203.0mg/dl respectively. The knowledge for diabetes and difficulty index in diabetes management changed from 8.13 to 9.10 and from 3.52 to 2.91 respectively, and these changes were the positive. We observed improvement in self-test of sugar level, foot management, oral hygiene and proper medication but not in self-test of nutritional management. Conclusions: This study revealed that the case management program for diabetic patients who were registered in NHIC is significantly effective. However, the program need to study further to understand its long-term effects.