Social demand for the disclosure of medical information is increasing, especially the treatment for unruptured intracranial aneurysms. This study investigated to what extent information on the treatment for unruptured intracranial aneurysms is disclosed on websites in Japan. We surveyed 1225 institutions authorized by The Japan Neurosurgical Society. The following factors were analyzed: percentage of institutions with websites, disclosure of number of surgeries, and disclosure of outcome of treatment for ruptured and unruptured intracranial aneurysms. Of the 1225 institutions surveyed, 1097 (89.6%) had their own websites. The total number of websites was 1262 since some institutions have several homepages in different websites. The annual number of surgeries was shown in 274 of the 1225 institutions (22.4%). The outcome of treatment for ruptured intracranial aneurysms was disclosed in 104 of the 1225 institutions (8.5%). The outcome of treatment for unruptured intracranial aneurysms was shown in only 32 of the 1225 institutions (2.6%). Disclosure of outcome of treatment for unruptured intracranial aneurysms on websites is not common. To improve disclosure of the outcome on websites, guidelines should be established.