Nonoperative management (NOM) for blunt splenic trauma (BST) is an established practice. The impact of splenic embolization (SE) in the algorithm for NOM has not been well studied. This study evaluates the role of SE and spleen injury grade on failure of NOM. Retrospective cohort of trauma registry over a 7-year period (2000-2006) for patients who suffered BST was studied. Data including demographics, splenic injury grade, and SE were recorded. Characteristics were compared between the successful and failed NOM groups. Kaplan-Meier, life table, and Cox-proportional hazard regression analyses were performed. Of the 499 patients who suffered BST, 407 (81.6%) patients had successful NOM and 92 (18.4%) patients failed NOM (including splenectomies performed within 1 hour of admission). Failed NOM group had a higher splenic injury grade compared with the successful NOM group (P < 0.0001). Seventy-five per cent underwent a splenectomy within 7.7 hours of admission. Nearly all grade I and II splenic injuries that failed NOM occurred by 24 hours. Grade 3 and 4 injuries that failed NOM occurred by 150 hours. SE was protective against splenectomy (Hazard Ratio (HR) 0.18, 95% confidence interval: 0.06-0.55, P = 0.004), whereas splenic injury grades III or higher was associated with increased risk of splenectomy (grade III: HR 5.26, P = 0.003; grade IV: HR 6.84, P = 0.002; grade V: HR 9.81, P = 0.002) compared with those with splenic injury grade I. Splenic embolization is a protective measure to reduce the failure of NOM. Spleen injury grade III and higher was significantly associated with NOM failure and would require a 5-day inpatient observation.