Infectious intracranial aneurysms: comparison of groups with and without endocarditis. A series of 12 patients with infectious intracranial aneurysms is presented, and a number of unusual features of the disorder are emphasized. A comparison of characteristics of the aneurysms and clinical course is made between patients with and without infective endocarditis. Most of the unusual characteristics of infectious aneurysms, including rare locations, causative organisms, and predisposing medical conditions, occurred in the group without endocarditis. The relationship of atypical features of infectious aneurysms to the etiology of aneurysm formation is discussed, and an approach to treatment is presented. 