Typical posterior pelvic fixation constructs use one or more large screws inserted from the lateral iliac cortex into the safe upper sacral ala or body. As a result of the deforming forces acting perpendicular to the implant axis, routine iliosacral screw fixation may not provide adequate stabilization, especially in certain unstable injuries. Longer iliosacral screws that traverse the entire upper sacrum and exit the contralateral iliac cortex may improve holding power and also stabilize concomitant contralateral posterior pelvic injuries. These transiliac-transsacral screws are reliably safe to insert using routine intraoperative fluoroscopy, and they provide durable fixation. These screws require careful preoperative planning and more precise technical attention during insertion because they pass through both sacral alar zones. Transiliac-transsacral screws may be particularly useful in the presence of osteoporosis, significant posterior pelvic instability including spinopelvic dissociation, patient obesity, anticipated noncompliant behavior, bilateral posterior pelvic injuries, and nonunion procedures.