OBJECTIVE To describe and evaluate the reliability and the accuracy of a specific computed tomography-based assessment in predicting treatment decisions for pure orbital floor blowout fractures (BOFs). METHODS In this retrospective cohort study, the charts of all patients presenting with isolated BOFs from January 2009 through April 2011 at the University Hospital of Geneva were reviewed. The systematic computed tomographic assessment included the following 3 parameters: 1) ratio of the fractured orbital floor; 2) maximal height of periorbital tissue herniation, and 3) a 4-grade muscular subscore describing the position of the inferior rectus muscle relative to the level of the orbital floor. The parameters' predictive value regarding the treatment decision (conservative vs surgical) was assessed by logistic regression and relative operating characteristic curves. RESULTS Forty-eight patients (24 male) were included. The patients' mean age was 49.5 years. The ratio of the fractured orbital floor, the maximal height of periorbital tissue herniation, and the muscular subscore were significant predictors in univariate analysis (P = .02, P = .006, P = .001, respectively), whereas, in a multivariate analysis, only muscular subscore remained a significant predictor (P = .003) and reached a similar predictive ability as the 3 parameters together. CONCLUSIONS The present study showed that the severity of inferior rectus muscle displacement is the most important independent predictive radiologic factor in the treatment decision-making process for pure BOFs. This systematic computed tomographic assessment is a valuable tool for a better understanding of BOF management overall. Further studies are needed to establish its clinical relevance.