SummaryThe purpose of this study was to determine whether orbital volume assessment by computerized tomography (CT) could provide additional information for the initial evaluation of orbital blowout fractures and guide optimal treatment. The medical records of 30 patients with orbital blowout fractures, either surgically or conservatively managed, were retrospectively reviewed. Orbital volumetric analysis was then determined from digitized CT scans. Fracture-related volume expansion relative to the unaffected fellow orbit was correlated with motility deficits and location and degree of enophthalmos. Early Hertel's measurements (<4 weeks) were available in 21 patients and did not correlate with the computer volumetric values or with subsequent late enophthalmos. Late Hertel's measurements (>4 weeks) were obtained in 13 of 15 nonrepaired fractures and in 5 of 15 surgically repaired patients (late presentation; 18 patients). When seen at more than 4 weeks, 11 (92%) of 12 patients with ≥13% orbital volume expansion manifested significant enophthalmos (>2 mm) compared with 1 (17%) of 6 patients with <13% orbital expansion (p= 0.004). Fractures presenting with enophthalmos on initial examination had extensive medial wall involvement in addition to the floor fracture (p= 0.003). CT measurements of orbital volume can predict the final degree of late enophthalmos and may facilitate the planning of surgical intervention.