Acute pelvic fractures are potentially lethal, even with modern techniques of poly-trauma care. The appropriate treatment of such fractures is dependent on a thorough understanding of the anatomic features of the pelvic region and the biomechanical basis of the various types of lesions. Although the anterior structures, the symphysis pubis and the pubic rami, contribute approximately 40% to the stiffness of the pelvis, clinical and biomechanical studies have shown that the posterior sacroiliac complex is more important to pelvic-ring stability. Therefore, the classification of pelvic fractures is based on the stability of the posterior lesion. In type A fractures, the pelvic ring is stable. The partially stable type B lesions, such as "open-book" and "bucket-handle" fractures, are caused by external- and internal-rotation forces, respectively. In type C injuries, there is complete disruption of the posterior sacroiliac complex. These unstable fractures are almost always caused by high-energy severe trauma associated with motor vehicle accidents, falls from a height, or crushing injuries. Type A and type B fractures make up 70% to 80% of all pelvic injuries. Because of the complexity of injuries that most often result in acute pelvic fractures, they should be considered in the context of polytrauma management, rather than in isolation. Any classification system must therefore be seen only as a general guide to treatment. The management of each patient requires careful, individualized decision making.