Sacral bar fixation is a well-recognized technique for the treatment of posteriorly unstable pelvic injuries, particularly sacral fractures. The sacral bars are placed in the iliac crest posterior to the sacrum. We reviewed 103 pelvic computed tomography (CT) scans and three cadaver pelves to measure the iliac crest prominence and its spatial relationship to the lamina of the sacrum. It was found that the best bony purchase for the bars is at the level of the L5-S1 junction. Lower placement of the bar increases the risk of violating the sacral canal and may also decrease the bony purchase of the bars. Some patients have an inadequate iliac crest posteriorly for proper placement; therefore, the pelvic CT scans should always be carefully evaluated preoperatively. The study also includes a description of a technique for percutaneous placement of sacral bars using fluoroscopic guidance.