Purpose This study was designed to analyze the outcomes of endovascular treatment for internal iliac artery aneurysm (IIAA) at mid-term follow-up. Methods We retrospectively analyzed 33 patients (28 males, mean age 77.4 years) who underwent endovascular treatment of 35 IIAAs (mean diameter 39.8 mm) from 2002 to 2012. We attempted to completely and selectively embolize all distal branches with permanent embolic materials, followed by proximal controls either by stentgraft placement (type 1) or coil embolization (type 2). Results Procedural success rate was 97.1 % (n = 34). Complete permanent distal branches embolization was achieved in 27 (79.4 %), type 1 in 24 (70.6 %), and type 2 in 10 (29.4 %) cases. During mean follow-up period of 29.1 months (range, 1.2-92.8), no IIAA-related mortality and stent/stent-graft related complications occurred. Pelvic ischemia occurred and resolved in 8 (25 %) patients. Among 32 cases followed by CT, the aneurysm diameter was stable in 18 (56.3 %), shrank in 11 (34.4 %), and enlarged in 3 (9.4 %) cases. In 22 assessed by contrast-enhanced CT, secondary endoleak occurred in 3 (13.6 %) cases and 2 required secondary interventions (2/32, 6.3 %). Type 1 procedure tends to have better mid-term outcomes. Incomplete permanent distal branches embolization was associated with enlargement and secondary intervention (p = 0.007 and p = 0.042, respectively). The secondary intervention-free rate at 3 years in the complete and incomplete distal embolization group was 100 and 83.3 %, respectively (p = 0.128). Conclusions Endovascular treatment for IIAA is feasible and safe. Complete permanent distal branches embolization is important to achieve satisfactory mid-term outcomes.