Temporal bone fractures can be difficult to detect clinically and radiographically. Air is sometimes present in the glenoid fossa of the temporomandibular joint (TMJ) at computed tomography (CT) of acute basilar skull fractures. This study evaluated TMJ fossa air as a sign of temporal bone fracture. Initial CT scans of the head in 114 patients with a diagnosis of basilar skull fracture at discharge were retrospectively reviewed. TMJ fossa air was present in 23 of 114 patients (20.2%) and was bilateral in three patients. Only temporal bone fractures were significantly (P less than .001) associated with TMJ fossa air. Temporal bone fractures were observed at CT in 23 of 26 cases of TMJ fossa air, but in three of 26 cases, TMJ fossa air was the only CT sign of clinically apparent temporal bone fractures. TMJ fossa air is associated with acute temporal bone fracture and may be the only CT sign of an otherwise inconspicuous temporal bone fracture.