To investigate the impact of intraoperative blood transfusion on outcomes in patients who had major thoracic and lumber posterior spine instrumentation surgery. Retrospective study included patients who underwent major spine surgery between 2013 and 2017. Patients' demographics, surgical charts, anesthesia charts, discharge charts and follow-up outpatient charts were reviewed. Data collection included: age, gender, BMI, Charlson Co-morbidity Index (CCI) scores, American Society of Anesthesiologists (ASA) scores, amount of estimated blood loss [% estimated blood volume (%EBV)], amount of blood transfused during surgery and post-surgery before discharge, number of fusion levels, pre- and postoperative hemoglobin (Hb) levels, and length of hospital stay. Also collected in-hospital postoperative complications (cardiovascular, pulmonary, infections and deaths). Patients' postoperative intubation status data documented. Reviewed follow-up charts to document any complications. Sample size = 289; No transfusion = 92; transfusion = 197. Transfused patients were significantly older, p < 0.001, higher average BMIs (p < 0.001); ASA scores (p < 0.001); CCI scores (p < 0.001), mean postoperative Hb level (p = 0.004), average intraoperative %EBV loss (p < 0.001), longer hospital stays (p = 0.003). Non-transfusion cohort had significantly higher proportion of patients (p < 0.001) extubated immediately after surgery. Seventeen patients had at least one in-hospital complication, p = 0.05. Complications were not significant among groups. Intraoperative blood transfusions and high volume intraoperative allogeneic blood transfusions did not increase risk for in-hospital complications or surgical site infections. Delayed extubations noticed in patients who received higher volumes of intraoperative allogeneic blood transfusions. High-volume intraoperative blood transfusions increased length of hospital stays. High post-hospital surgical infections associated with high volume intraoperative blood transfusions. Results should be interpreted cautiously due to small sample size.