Study Design: Cohort study. Objectives: To report the two-year revision risk following primary adult spinal deformity (ASD) surgery, describe reasons for revisions, and assess risk factors for revision surgery. Summary of Background Data: Revision risk following primary ASD surgery has been reported to vary between 7% and 26%, but with loss to follow-up as a considerable challenge. Methods: Patients ≥18 years of age undergoing primary instrumented surgery for ASD in Denmark during 2006–2014 were identified by procedure and diagnosis codes in the Danish National Patient Registry (DNPR). Complete two-year follow-up on revision surgery for each patient was achieved. Medical records were reviewed to determine reasons for revisions. Overall comorbidity was summarized using the Charlson Comorbidity Index (CCI) based on DNPR data; low comorbidity (CCI 0); medium comorbidity (CCI 1–2); and high comorbidity (CCI ≥3). Risk factors for revision were assessed in a Cox regression model. Results: A total of 553 patients were identified. Of these, 19.9% were revised within the two-year follow-up and 7.2% of patients were revised more than once. Median time to revision was 308 days (interquartile range 105–508). The most common reason for revision was implant failure (38.2%) followed by infection (11.8%). Increased age (hazard ratio [HR] = 1.13, 95% confidence interval [CI] 1.01–1.26, per 10 years increment) and high comorbidity burden (HR = 2.10, 95% CI 1.16–3.79) were associated with increased revision risk. Risk of revision increased from 2006 to 2014; hence, year of primary surgery (with 2006 as reference) was associated with increased revision risk (HR = 1.09, 95% CI 1.01–1.18). Conclusions: The revision risk within 2 years after primary ASD surgery was 19.9% nationwide in Denmark, and implant failure was the most common reason for revision. Increased comorbidity and age were separately associated with increased risk of revision. Level of Evidence: Level II.