Sacral fracture is a difficult diagnosis due to the lack of specific signs and the inaccuracy of conventional radiology. This kind of fracture affects either polytraumatised or aged patients, in whom the fracture can be diagnosed. However these fracture have to be recognized because of their potentially adverse consequences, particularly on neurological structures. The case of a 56 years old man who fell from his height is reported. Two weeks later, due to mild neurologic symptoms, an X-ray and CT of the pelvis were performed, showing a fracture of both sacral alae. A complex neurologic sensitive and motor impairement appeared involving S1 to S5 levels on the left side and L2 to S5 levels on the right side. Many investigations were done to rule out any other etiologic factor of this complex and progressive neurologic deficit. The probable cause was an iterative stretching of the lumbosacral roots ambulating with a floating sacrum fracture.