We created a decision analysis model of the nonsurgical management of traumatic splenic injuries to clarify the risk of hospital survival, overwhelming postsplenectomy infection (OPSI) deaths, and transfusion-related deaths. We reviewed 72 cases of splenic injury at our institution to identify our transfusion requirements for successful observation (0.5 units), observation failure (1.0 units), and surgical splenic management (1.6 units). Using our model and baseline probabilities determined from the literature, we compared the nonsurgical management of splenic injuries with immediate laparotomy and found an increase in hospital survival with observation, but an over two-fold increase in the risk of transfusion-related death. The OPSI deaths were not markedly different between the two strategies. Overall, we found decision analysis useful in identifying important variables such as the probability of nontherapeutic laparotomy death or missed injury, and in clarifying the risk of the nonsurgical management of splenic injuries with regard to transfusion-related deaths and OPSI deaths.