PURPOSE: There have been controversies about the management of small abdominal aortic aneurysm (AAA). This prospective study was performed to analyze the annual expansion rates and the clinical courses of small AAAs, and to we wanted to suggest some guidelines for the proper management of small AAAs in Koreans. METHOD: From 1991 to 2003, thirty-five patients who had an initial diagnosis of small AAA were enrolled into the study group. All the patients were assigned to undergo regular imaging studies with either ultrasonography or CT angiography every 6 months. At the end of the study, the twenty four patients who were followed up with at least three successive visits were included in the statistical analysis. The clinical symptoms and the size of their aneurysms were documented on each visit. Symptomatic aneurysms and aneurysms with a size greater than 5.5 cm were considered as candidates for surgical repair. The annual expansion rate, rupture rate and the requirements for aneurysm repair were analyzed. The overall aneurysm expansion rate was 0.33+/-0.22 cm/year. RESULT: The expansion rate of the aneurysms smaller than 4.0 cm (12 cases) was 0.32+/-0.26 cm/year and that of aneurysms between 4.0 cm and 5.0 cm in size (12 cases) were 0.34+/-0.19 cm/year (P=0.55). Only the presence of iliac artery involvement was significantly related with a higher aneurysm expansion rate (0.47+/-0.2 cm/year vs. 0.19+/-0.13 cm/year, respectively, P=0.001). There was no rupture of aneurysm during the study. 10 cases undergone aneurysm repair and there was no morbidity or mortality after the aneurysm repair. CONCLUSION: Small AAAs in Koreans can be safely managed with regular follow-up. Closer follow-up is recommended as the aneurysm size increases and for small aneurysms that involve the iliac artery.