Three elderly patients with incapacitating back and leg pain were found to have spontaneous osteoporotic fractures of the sacrum. The clinical picture in these three patients suggests a distinct clinical entity of spontaneous osteoporotic fracture of the sacrum (SOFS). This is characterized by severe low back, hip, and leg pain that suggests initially lumbosacral radicular compression, either from disk disease, spinal stenosis, tumor. However, objective mechanical signs more typical of those entities may be absent or minimal in SOFS. Symptoms suggestive of a cauda equina syndrome may be present, but there is minimal or no neurological deficit on examination. Marked sacral tenderness is a hallmark of SOFS.