Sacral fractures are rare injuries that are often neglected because of the general severity of the patient's injuries. They are typical injuries in patients with polytraumata. A "hidden" injury, they are often diagnosed late or are even missed. In a well-documented consecutive series of 1,350 patients with pelvic fractures treated in the trauma department of the Hannover Medical School between 1972 and 1991, a total of 377 sacrum fractures were evaluated in a retrospective study. The cause of the accident, mechanism of injury, concomitant injuries, diagnostic procedures, classification of the pelvic injury (TILE), as well as the classification of the sacrum injury (DENIS), treatment and outcome were analyzed in all cases. Observed complications with special attention to injuries to the lumbosacral plexus were correlated with the classification of the sacrum and pelvis, as well as with a detailed analysis of the fracture pattern and fracture characteristics. In 89.4% at least one additional body region was injured in these patients. PTS (Hannover Polytrauma Score) groups III and IV included 42.5% of the patients. With an improved diagnostic protocol (radiological a.p. views, oblique views and CT scan), the observed rate of sacrum fractures was 33%. Neurological deficits occurred in 15.1% of the patients. In contrast to the literature, the rate of neurological deficits was related more to the degree of pelvic instability (TILE) than to the specific fracture pattern in the sacrum. In stable injuries (TILE A) neurological deficits were only seen in exceptions. In type B injuries the maximum rate was 10%, whereas in unstable fractures (TILE C) the rate of neurological deficits was 32.6% in transalar fractures (DENIS zone I), 42.9% in transforaminal fractures (DENIS zone II), and 63.6% in central fracture types (DENIS zone III). Additional risk indicators for neurological impairment are avulsion fractures of the sacrum, comminuted and bilateral fracture lines. The fracture classification should thus be modified. Our own experience with operative therapy for sacral fractures (open revision of the sacral plexus together with internal stabilization of the fracture) is still limited, but based on the experience presented, further development of the treatment protocol for sacrum fractures should be considered.