The aim of this study was to review the natural history of symptomatic intramedullary spinal cord (IMSC) cavernous malformations in order to analyze the underlying mechanisms leading to symptoms and determine the potential risk of lesional hemorrhage. Between January 1990 and June 2001, ten consecutive patients with IMSC cavernous malformations were treated surgically in our institution. Age ranged from 17 to 73 years (mean 34.5). All patients became symptomatic due to one or more hemorrhages leading to neurological deficits of different severity, with a more aggressive course for upper cervical lesions. Pre- and postoperative patient condition was classified according to the Frankel scale. Four patients experienced one hemorrhage, four patients two, one patient three, and another one five repeated hemorrhages. The annual retrospective hemorrhage rate for symptomatic IMSC cavernous malformations was 4.5% per patient/year, with a prospective rehemorrhage risk of 66% per patient/year. The postoperative condition was improved in four patients and unchanged in six, and none grew worse. Detailed analysis of history and clinical course in all patients revealed an acute onset of symptoms with subsequent neurological deterioration after each bleeding episode. Based on the significant risk of rehemorrhage and the gratifying functional results, surgery is indicated for symptomatic IMSC cavernous malformations.