Background: The purpose of this study was to evaluate the effectiveness of telephone call reminder on retention rate in obese patients. Methods: A total of 118 patients (85 first-time visitors, 33 re-visitors), who visited an obesity management clinic from May 2003 to May 2004, were divided into the intervention group (n=64) and the comparison group (n=54). The intervention was a telephone call reminder before the appointment date. The retention rate up to 7th visit and body mass index were compared between the two groups. Results: The retention rate was 64.4% at 4th visit (after 66.5+/-29.2 days from the first visit) and 36.4% at 7th visit (after 142.1+/-57.8 days from the first visit). For the first- time visitors, the retention rate at 3rd visit was significantly higher (85.1%) in the intervention group than those in the comparison group (67.6%, P=0.049). Otherwise, there were no significant differences in retention rate and body mass index at each visit between the two groups regardless of the visiting status. However, the body mass index at 4th and 7th visit was significantly lower in the intervention group than in the comparison group among the first-time visitors who completely attended 7 times (P=0.031). Conclusion: We could not find the telephone call reminder to be an effective method to improve retention rate in obesity management clinic. Further intensive approach is needed to promote attendance.