The authors report 18 cases of surgically proved spontaneous epidural hematoma of the lumbar spine. The clinical findings in spontaneous epidural hematoma were identical to those in acute disk herniation. Underlying disk abnormalities were common; the majority of hematomas (14 of 18, 78%) were associated with small concomitant disk herniations or underlying annular tears. The magnetic resonance imaging and computed tomographic findings were similar to those in extruded/free-fragment disk herniation. The strong coincidence between epidural hematoma and underlying disk disruption (annular tear or herniation) leads the authors to postulate that spontaneous epidural hematoma results from tearing of fragile epidural veins lying adjacent to the displaced anulus or nucleus.