Pure trigeminal motor neuropathy is a trigeminal motor paralysis unaccompanied by signs of trigeminal sensory or other cranial nerve involvement. We present a case of a 38-year-old man complaining of progressive weakness and wasting of the right masticatory muscles after a bout of mild cold symptoms. No sensory symptoms were present. History, neurologic examination, electrophysiologic studies, and magnetic resonance imaging of the brain led to the diagnosis of pure trigeminal motor neuropathy. The cause may have been an autoimmune reaction to a viral infection.