Methods: A prospective analysis of 2,860 admissions was performed over 1 year in a tertiary care orthopedic hospital. All unscheduled readmissions following spine surgery within 90 days of discharge were included, irrespective of type or location of surgery. Polytrauma, primary osseous infections, and planned readmissions were excluded. Results: Our readmission rate was 3.32% (95/2,860). Leading readmission causes were surgical site infections (SSIs) accounting for 44.21% (n=42; superficial, 23; deep, 11; organ and space, 8), followed by aseptic pain 31.58% (n=30) and medical causes 13.68% (n=13). Though 86.95% of superficial SSIs occurred within 30 days, 21.1% of deep SSIs occurred beyond 30 days. During the 30–90-day interval, 33.68% of readmissions occurred. The financial burden amounted to 41,93,660 Indian Rupees, and the mean bed-days lost was 7.33 per readmission. Hospital stay ≥10 days, health insurance, and comorbid illnesses (diabetes, hypertension, and liver disease) were associated with readmissions (p<0.05). Conclusions Our study showed that SSIs and aseptic pain were the leading causes of readmissions at 90 days after spine surgery. Limiting the analysis to 30-day readmissions as in previous studies would lead to failure in the identification of more severe complications like deep SSIs. Continued vigilance, particularly for patients with predisposing factors, could help alleviate the financial burden.