OBJECTIVE: We aimed to investigate the effect of coiling for small unruptured intracranial aneurysms (UIAs) (<5 mm) on progressive occlusion and recanalization, and the dubious factors related to progressive occlusion and recanalization among UIAs without complete occlusion. METHODS: A total of 264 patients with 287 small UIAs were coiled in our institution between June 2009 and December 2014. All UIAs were divided into small (3-5 mm) and very small (<3 mm) groups, and UIAs without initial complete occlusion were divided into progressive, stable, and recanalization groups. Baseline characteristics, procedure-related complications, angiographic follow-up results, and clinical outcomes were statistically analyzed. RESULTS: Among 287 aneurysms, 211 aneurysms (73.5%) were completely coiled, 3 (1.2%) had intraoperative ruptures, and 12 (4.2%) had perioperative thromboembolic events. Angiographic follow-up was available for 174 patients (65.9%), and the incidence of recanalization was 5.7%. Among 56 aneurysms without complete occlusion, 43 (76.8%) had progressive occlusion and 6 (10.7%) had recanalization. Anatomic results of initial and follow-up between the small and very small groups were similar. On logistic regression analysis, smaller size (<3 mm) without complete occlusion related to recanalization (odds ratio, 8.0, 95% confidence interval 1.3-50.0; P = 0.026). CONCLUSIONS: Our study suggested that coil embolization of small UIAs can achieve a high rate of progressive occlusion and a low rate of recanalization during follow-up. Anatomic results of initial and follow-up between small (3-5 mm) and very small (<3 mm) groups were similar. Smaller size (<3 mm), without complete occlusion, may relate to recanalization.