Pre-surgical psychological assessments are becoming common in the United States and are recommended or required prior to surgical/spinal cord stimulator intervention for chronic back pain. Psychological testing is often recommended for these evaluations and the various versions of the Minnesota Multiphasic Personality Inventory (MMPI) have demonstrated utility for predicting outcomes in this setting. This investigation sought to extend that literature with the newest version of the MMPI, the MMPI-3. The sample comprised of 909 patients (50.5% men, 49.5% women) who consented to participating in an outcome study and took the MMPI-3 along with other self-report measures of pain, functional disability, and emotional functioning prior to surgery as part of their pre-surgical psychological assessment. Self-report measures of pain, functional disability, and emotional functioning were administered again one-year following the intervention. MMPI-3 scale scores accounted for up to 9% of additional variance in the outcomes after controlling for pre-surgical measures. Measures of emotional/internalizing dysfunction, somatic dysfunction, and, to a lesser extent, behavioral/externalizing dysfunction contributed the most to the prediction of poorer outcomes.