PURPOSE: Orbital floor injuries can occur in isolation or in association with zygomatico-maxillary complex (ZMC) fractures. Volumetric CT measurements of affected orbits are investigated for utility in guiding management in these two groups. METHOD: The medical records of all patients with craniomaxillofacial (CMF) injuries(2003-2005) were reviewed. Of 522 total patients, there were 45 patients with isolated orbital floor fractures, 13 underwent repair (28%); 64 patients with ZMC fractures, 36 underwent reconstruction (56%), and 10 underwent orbital floor repair (15%). Preexisting (prospective) radiographic criteria for floor exploration included 50% area fracture in isolated injuries and 10mm estimated ZMC compression in ZMC-associated floor injuries. Volume measurements of the affected orbits were obtained and compared to the contralateral orbit, which served as controls using Image Segment. From segmented data, polygon models were fit to render three dimensional images for volumetric and dimensional analysis. RESULTS: Pre-treatment in the operative ZMC group, there was an average decrease in orbital volume of 18.3%. In the isolated orbital floor group, there was an average increase in orbital volume of 28.3 %. In the nonoperative ZMC group there was an average decrease in volume of 3.3%. CONCLUSION: ZMC-associated orbital floor injuries can be compressive injuries associated with loss of volume, while isolated injuries generally result in volume expansion. Radiographic criteria are often considered in the decision to proceed withorbital floor exploration to avoid late enophthalmos. The literature suggests that a 20% change in orbital volume results in perceptible deformity. Therefore, a radiographic criterion of 50% floor area (28% volume increase) in isolated injuries may be too stringent; an estimated 10mm of compression (18.3% volume change), is a reasonable operative criterion for floor exploration in ZMC-associated injuries.