This study was performed to investigate the effect of a telephone-delivered intervention on glycemic control and body mass index in Korean type 2 diabetic patients. 38 patients were randomly selected, with 20 assigned to a telephone group and 18 to a control group. The goal of the intervention was to keep blood glucose concentrations close to the normal range. The intervention was applied to the telephone group for 12 weeks. It consisted of continuous education and reinforcement of diet, exercise and medication adjustment, as well as frequent self-monitoring of blood glucose levels. Telephone intervention was performed twice per week for the first month, and then weekly for the second and third months. Subjects were requested to write self- management logs, including blood glucose, diet and an exercise diary. The diet diaries were analyzed by a dietitian, and subjects instructed about the results by telephone counseling or mail. All medication adjustments were communicated to the subjects' diabetes specialist. Glycosylated hemoglobin (HbA1c), fasting blood glucose (FBG) and 2-hour postprandial glucose were measured before, and after, the intervention. Patients in the telephone group had a mean decrease of 1.2%, with those in the control group having a mean increase of 0.6%, in HbA1c. There were no significant differences in the body mass index (BMI) between the two groups. These findings indicated that a telephone-delivered intervention would improve HbA1c, but would not affect BMI.