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STUDY DESIGN We retrospectively analyzed Spinal Instability Neoplastic Score (SINS) in 110 patients with prostate cancer operated for metastatic spinal cord compression. OBJECTIVE We aimed to investigate the association between SINSs and clinical outcomes after surgery for metastatic spinal cord compression (MSCC) in patients with prostate cancer. SUMMARY OF BACKGROUND DATA The SINS is a useful tool for assessing tumor-related spinal instability, but its prognostic value regarding survival and neurological outcome is still controversial. METHODS We analyzed 110 consecutive patients with prostate cancer who underwent surgery for MSCC. The patients were categorized according to their SINSs. Patients with castration-resistant prostate cancer (CRPC, n = 84) and those with hormone-naïve disease (n = 26) were analyzed separately. RESULTS In total, 106/110 patients met the SINS criteria for potential instability or instability (scores 7-18). The median SINS was 10 (range 6-15) for CRPC patients and 9 (7-16) for hormone-naïve patients. In the CRPC group, the SINS was classified as stable (score 0-6) in 4 patients, as potentially unstable (score 7-12) in 70 patients, and as unstable (score 13-18) in 10 patients. In the hormone-naïve group, 22 patients met the SINS criteria for potential instability and 4 patients for instability. There was no statistically significant difference in the overall risk for death between the SINS potentially unstable and unstable categories (adjusted HR 1.3, p = 0.4), nor in the risk of loss of ambulation one month after surgery (adjusted OR 1.4, p = 0.6). CONCLUSIONS The SINS is helpful in assessing spinal instability when selecting patients for surgery, but it does not predict survival or neurological outcomes. Patients with a potential spinal instability benefit equally from surgery for MSCC as do patients with spinal instability. LEVEL OF EVIDENCE 3.