The authors used a micromirror under a microscope with an indocyanine green (ICG) imaging system to assess clipped aneurysms and the blood flow in hidden regions during aneurysm surgery. This study then investigated the usefulness of such mirroring with ICG angiography (MICGA). A micromirror was used during aneurysm surgery on 25 patients, and MICGA was performed on 10 of these 25 patients to inspect the hidden region after clipping. The mirrored aneurysms were located at the posterior communicating artery (n = 4), anterior choroidal artery (n = 4), proximal A1 segment (n = 1), and middle cerebral artery (n = 1). In all 10 cases, MICGA was successful in assessing the state of the clipped aneurysm and blood flow of the vessels in the hidden region after clipping. This led to clip repositioning in 3 patients (30.0%) because of incomplete clipping of a hidden aneurysm or occlusion of a hidden perforator. Complete occlusion of the aneurysm was achieved in 8 patients, and the other 2 patients showed near complete occlusion because of an intentional residual aneurysm to avoid a small vessel adherent to the posterior wall of the aneurysm base. MICGA can provide useful and reliable information on the state of a clipped aneurysm and the blood flow of associated vessels and perforators in a hidden region after aneurysm clipping.