OBJECTIVE Cone-beam computed tomography (CBCT) offers the advantage of a 3-dimensional representation of the anatomic relationship of the mandibular third molar tooth and the inferior alveolar canal (IAC), as compared to a panoramic radiograph. We hypothesized that a novel method of categorizing the degrees of compression of the IAC were reliable predictors for postoperative nerve injuries. METHODS We conducted a retrospective analysis of the outcomes in third molar surgery for patients who obtained a CBCT scan in additional to a plain film radiograph over a 12 months period and underwent surgical removal of their mandibular third molars; 257 consecutive patients were identified, and 416 mandibular third molars were surgically removed. RESULTS Patients who had severe compression of the inferior alveolar canal (IAC) on CBCT imaging had a significantly increased risk of a postoperative IAN injury (P = .0068, OR = 3.47, 95% CI: 1.40 to 8.54) and accounted for 52.17% of all IAN injuries. Ninety-one percent of all cases of postoperative nerve injury occurred in female patients. The mean age of patients with a postoperative IAN injury (30.2 years) was significantly higher than those without injury 26.0 years; (P = .016, 95%CI: 25.11 to 33.80) CONCLUSIONS: In addition to patient factors, assessment of the degree of compression on a preoperative CBCT image is a useful tool for predicting outcomes in mandibular third molar surgery. In cases of severe compression of the IAC, patients are at a significantly increased risk of postoperative IAN injury.