Operative management of unstable pelvic fractures is directed toward stabilization of the posterior lesion. We describe a technique of posterior pelvic fixation that uses a 4.5-mm reconstruction plate as a transiliac tension band. The plate is inserted through the posterior superior iliac spines with screw fixation to the ilium. Our initial clinical experience was gained using this technique in 15 patients who had unstable pelvic ring injuries with sacral fractures. Stable fixation was achieved in all patients with this low-profile plate. There were no infections, no wound complications, and no failures of fixation. Comparative biomechanical testing using cadaveric and artificial pelvises demonstrated that the strength of the transiliac plate method was equal to that of other techniques of posterior pelvic fixation.