OBJECTIVE: Delayed bleeding of unruptured intracranial aneurysms (UIAs) after coil embolization is rare; this study aimed to analyze the occurrence of delayed bleeding of UIAs after coil embolization. METHODS: We retrospectively analyzed patients with UIAs after coil embolization between January 2002 and December 2018 and assessed the features of UIAs with delayed bleeding after coil embolization. RESULTS: Analysis included 307 patients with 335 UIAs. Mean follow-up was 7.1 ± 4.9 years, and total follow-up was 2365 aneurysm-years. There were 271 (80.9%) aneurysms located in the anterior circulation and 64 (19.1%) aneurysms located in the posterior circulation. Significant differences were observed between the 2 groups in terms of maximum size of the aneurysm (P < 0.01), width of the aneurysm neck (P < 0.01), and number of retreatment cases (P < 0.01). During the follow-up period, delayed bleeding occurred in 4 aneurysms (annual bleeding rate of 0.17%); all were located in the posterior circulation. The original size was not relatively large (mean 8.6 ± 2.4 mm). All aneurysms bled within 5 years (mean 35 ± 9.6 months) after the initial treatment. Two were de novo aneurysms that developed adjacent to the coiled aneurysms and were not detected on follow-up magnetic resonance angiography. CONCLUSIONS: Cautious follow-up of UIAs with digital subtraction angiography is important, articularly within the first 5 years after the procedure. If there are changes in the anatomic outcomes, short-term reassessment or additional treatment should be actively considered, particularly for aneurysms in the posterior circulation.