Various systems of supplementing bone grafts with internal fixation in the lumbosacral spine have been used in an effort to improve fusion rates. This study reports biomechanical data of cyclic loading cadaveric spines instrumented with translaminar facet screws as well as early clinical results on this technique. Static loading tests comparing uninstrumented and instrumented spinal motion units show that a ninefold increase in flexion load is necessary for constant displacement after facet screw fixation. Repetitive loading tests show only a small decrease in stiffness of instrumented segments even after 5,000 cycles. To date, 35 patients have undergone fusion by this technique as performed by one surgeon. After excluding Workers' Compensation cases and cases with less than 2 years follow-up, there were 18 cases available for review. Twelve of these 18 cases were two-level fusions. Ten patients underwent concomitant discectomy or nerve root decompression. There were no cases of iatrogenic neurologic injury or pseudoarthrosis. It is concluded that translaminar facet screws have a sound biomechanical basis and are a valuable addition to lumbar fusion procedures.