Previous bleeding from a cerebral aneurysm indicates a higher risk of rupture. Hemosiderin may be detected during aneurysm surgery or by preoperative imaging sensitive to hemosiderin. The detection of hemosiderin deposits by T₂*-weighted magnetic resonance (MR) imaging was evaluated in 49 patients with unruptured cerebral aneurysms who underwent open surgery. MR imaging was performed using 3.0 tesla MR scanner. Two sequences of T₂*-weighted imaging, and proton density images were obtained. Preliminary study in patients with old subarachnoid hemorrhage provided the definitions of likely pathological findings during surgery and on T₂*-weighted imaging due to previous hemorrhage. Hemosiderin deposits in the subarachnoid space were observed during surgery in 9 of the 49 patients, although no obvious rupture site was detected around the aneurysm wall. Size, presence of bleb, location, and number of aneurysms showed no significant difference between patients with and without hemosiderin deposition. Hypointense areas on T₂*-weighted imaging were recognized in four patients. The mean size of the aneurysms in these patients was 9.8 mm, significantly larger than those in other patients (p = 0.029). Hemosiderin deposits were observed during surgery in sites close to the lesions on T₂*-weighted imaging in two of these four patients. Hemosiderin deposits are not rare in patients with unruptured aneurysms, and preoperative T₂*-weighted imaging can detect such deposits.