Trigeminal neuralgiais a chronic facial pain classified as a neuropathic pain. There is widespread agreement regarding the International Association for the Study of Pain definition of classical idiopathic trigeminal neuralgia as “a sudden, usually unilateral, severe, brief, stabbing, recurrent pain in the distribution of one or more branches of the fifth cranial nerve.” However, there are variations in presentation that are less easy to diagnose and an erroneous diagnosis of trigeminal neuralgia is occasionally made. In patients with tumors or multiple sclerosis, trigeminal neuralgia is termed secondary. Currently, clinical manifestations are the mainstay for diagnosis because there are no objective tests to validate the diagnosis. The sensitivity and specificity of these clinical manifestations is reviewed. Magnetic resonance imaging (MRI) and three-dimensional fast-in-flow with steady-state precession MRI are performed to determine the presence of tumors or plaques of multiple sclerosis and to assess possible compressions and deformations of the trigeminal nerve. Their specificity and sensitivity regarding compressions found at the time of surgery is reviewed. Other differential diagnoses for chronic unilateral orofacial pain are discussed.