Purpose: To assess the association between preoperative S-albumin and postoperative outcome following adult spinal deformity (ASD) surgery. Methods: All patients undergoing ASD surgery from February 1, 2017 and January 31, 2018 at a single quaternary referral center were prospectively included. Adverse events (AE) during admission were assessed using the Spine AdVerse Events Severity (SAVES) system. Based on preoperative S-albumin, patients were categorized as “normal” or “abnormal” and compared regarding postoperative outcome, adverse events (AEs), 30- and 90-day readmission, revision surgery, and mortality. Results: A total of 128 patients aged ≥ 18 years were included, and S-albumin was available in 88%. Of these, 73% (n = 93) were classified as “normal”, 16% (n = 20) as “abnormal”, and 12% (n = 15) as “missing”. The “normal” albumin group had less comorbidity burden [ASA score 2 (2, 3) vs 3 (2, 3), p = 0.011], higher hemoglobin levels (8.4 (± 0.9) mmol/L vs 7.4 (± 1.1) mmol/L, p < 0.001), and higher S-albumin (38.9 (± 2.7) g/L vs 31.9 (± 4.4) g/L, < 0.001). The rate of 90-day readmission was significantly increased in the “abnormal” group (65% vs 36%), corresponding to a relative risk increase of 1.25 (95% CI 1.02–1.52, p = 0.029). Similar increased risks were found in subsequent logistic regression analyses, although results were not significant in multivariable analysis (p = 0.102). Comparing remaining outcome parameters, point estimates revealed increased AEs, 30-day readmission, and revision in the “abnormal” albumin group, although effects did not reach statistical significance. Conclusions: In a prospective, consecutive, single-center cohort of 128 patients undergoing ASD surgery, we found a significant association between “abnormal” preoperative S-albumin and increased 90-day readmission. Furthermore, although the findings were not statistically significant, we did find that AEs, 30-day readmission, and revision were numerically more frequent in the “abnormal” group, suggesting an expected tendency that should be further investigated. We conclude that nutritional status prior to ASD surgery could be important to consider and suggest validation in larger prospective cohorts. Level of evidence: Prognostic II.