The authors reviewed the early complications in all patients fused to the sacro-pelvis using Cotrel-Dubousset instrumentation at the Texas Scottish Rite Hospital. Sixteen patients were studied with an average follow-up of 13 months. Three methods of sacro-pelvis fixation were evaluated: iliosacral screws, sacral screws, and a technique whereby the caudle ends of the Cotrel-Dubousset rods were fashioned and inserted into the posterior iliac crest using the Galveston technique. Seven of the 16 sets of sacral screws (44%) failed during and after surgery. Two of the 7 sets of iliosacral screws failed postoperatively (28%). No failures occurred in the 8 sets of Cotrel-Dubousset rods placed with the Galveston technique. Seven of the nine medical complications observed (77%) occurred in the sacral screw group. Using calf spines, a biomechanical evaluation of each system was undertaken to determine strength of fixation. Each system was failed in flexion 3 times. The sacral screws were the weakest, pulling directly out of the sacrum at 40 N-M. Cotrel-Dubousset rods inserted with the Galveston technique were the strongest, experiencing rod deformities before flexion failure at 70 N-M. Iliosacral screws were of intermediate strength failing by rotation on the axis of the screws or pulling directly out of the ilium at 55 N-M. The authors conclude that using Cotrel-Dubousset rods inserted with the Galveston techniques was the strongest and safest method of sacro-pelvis fixation of the three tested.