Two siblings, a sister at age 3 years and a brother (15 years later) at 4 years of age, both presented with similar clinical pictures consisting of back pain, progressive gait difficulty, lower extremity weakness and hyperreflexia. Imaging studies in both cases showed the presence of a perimedullary mass with expansion of the bony spinal canal at T10-T12. Angiography demonstrated almost identical vascular lesions that in each case was being fed by a single left-sided T8 fistulous vessel that expanded into a giant perimedullary venous pseudoaneurysm. Each malformation was successfully obliterated using endovascular techniques, balloon occlusion of the feeding vessel in the first case and coil embolization of the pseudoaneurysm in the second. Following treatment the neurologic deficits resolved in both patients. These young siblings represent the first known case of familial occurrence of very similar giant perimedullary venous pseudoaneurysms of the thoracic spinal cord.