Thirty-seven patients with 44 intracavernous carotid artery aneurysms (ICCAAns) were seen at one institution from 1976 through 1988. Fifteen patients had multiple intracranial aneurysms and 7 had bilateral ICCAAns. Age at diagnosis ranged from 15 to 80 (median 61). Thirty patients were women. Sixteen had a history of hypertension. In 34% of patients the ICCAAns were asymptomatic at diagnosis, 36% were associated with headache, and 57% had associated signs or symptoms of mass effect including sixth nerve paresis (43%), trigeminal pain or sensory loss (32%), third nerve paresis (20%), decreased vision or visual field cut (18%), fourth nerve paresis (16%), and Horner's syndrome (7%). In 4 patients the ICCAAns ruptured, leading to subarachnoid hemorrhage in 3 and epistaxis in 1. Two patients with ICCAAns were seen with spontaneous thrombosis of the ipsilateral internal carotid artery leading to distal ischemic symptoms in 1. More than 90% of the ICCAAns were saccular. Thirty-four percent were small (less than 1 cm), 48% were large (1 to 2.5 cm), and 16% were giant (greater than 2.5 cm). The majority arose from the anterior genu of the intracavernous internal carotid artery, followed in frequency by the horizontal segment, and then the posterior genu. Magnetic resonance imaging is superior to computed tomography for diagnosing ICCAAns and is the screening procedure of choice. Angiography remains the "gold standard" for diagnosis and determining specific anatomic details necessary to plan therapy. Analyzing the radiographic anatomy of 44 ICCAAns. we conclude that theories attributing the origin of aneurysms to arterial bifurcations may be inadequate to explain the point of origin and direction of take off of up to one-fourth of ICCAAns.