The characteristics of mycotic aneurysms have changed since Osler first used the term in 1885. Sixteen mycotic aneurysms encountered between 1970 and 1973 were critically reviewed with regard to location, etiologic factors, microbial organisms, and methods of treatment. Peripheral aneurysms were seven times more frequent than aortic mycotic aneurysms. Pseudoaneurysms from trauma or vascular operations with concomitant infection were the most frequent types of mycotic aneurysms. Staphylococcus and Enterobacter were the most common organisms cultured. The anaerobes, Bacteroides and Peptostreptococcus, as well as Candida were also isolated. Ligation of the artery was distinctly superior to suture or graft repair in controlling infection and preventing rebleeding. Appreciation of the changing patterns of mycotic aneurysms will facilitate prompt diagnosis and proper treatment.