Objectives: Postsplenectomy vaccination (PSV) in an austere environment to minimize overwhelming postsplenectomy infection is challenging. We evaluated the clinical impact of a March 2008 clinical practice guideline (CPG) dictating immediate PSV at North American Treaty Organization Role 3 medical treatment facilities and subsequent complications. Methods: Utilizing U.S. military medical databases, we characterized all U.S. patients with a splenic injury from November 2002 to January 2012 by their surgical management: laparotomy with splenectomy (LWS), laparotomy without splenectomy, or nonoperative management. Relevant data including demographics, vaccinations, and documented bacterial and fungal isolates were obtained. Results: LWS comprised 63.6% of the 409 patients with a splenic injury from 2002 to 2012. The implementation of the PSV CPG improved overall vaccination compliance from 48.9% pre-PSV CPG to 86.9% post-PSV CPG (p < 0.01). It was found that 1.3% (2/159) of completely vaccinated LWS patients compared with 0% (0/101) of the incompletely vaccinated LWS patients had Streptococcus pneumoniae isolates in 391.0 and 251.4 follow-up years, respectively (p = 0.52). No Neisseria meningitidis or Haemophilus influenzae isolates were identified. Conclusions: PSV CPG implementation improved theater vaccination without increasing the incidence of encapsulated organisms.