The advent of magnetic resonance (MR) imaging has permitted the recognition of many angiographically occult vascular malformations before the development of complications and subsequent surgical removal. This study reviews all patients at one institution who had radiographically identifiable vascular malformations believed to represent cavernous angiomas in order to obtain information on the natural history of this particular lesion. All 8131 craniospinal MR images performed at our medical center from January 1, 1986, to November 30, 1989, were reviewed, and 32 patients were identified with 76 lesions meeting the MR imaging criteria for cavernous angioma. Medical histories, physical examination records, and other data from these patients were then reviewed to determine the frequency of complications. Their mean age at latest follow-up examination (or at surgical removal of the lesion) was 37.6 years (range 16 to 72 years). Sixteen patients (50%) had a history of seizures, seven (22%) had focal neurological deficits, and three (9%) had clinically significant hemorrhage attributable to the cavernous angioma; six patients (19%) were asymptomatic. The estimated risk of hemorrhage for this population is 0.25%/person-year of exposure; the estimated risk of seizure development is 1.51%/person-year. Eight patients underwent surgical procedures, resulting in improved seizure control and/or lessened neurological deficit. Although these lesions are often excised with relative ease and minimal morbidity, the potential risks and benefits of surgery must be weighed carefully before removal of these relatively benign malformations.