The diagnosis of primary hemifacial spasm (pHFS), due to a benign compression of the facial motor nerve by a vessel, within or close to its root exit zone, is often made with delay. Misdiagnosis includes psychogenic spasm, tics, facial myokymia or blepharospasm, but in fact post-facial palsy synkinesis (post-paralytic HFS) is the closest clinical condition, because it is limited to the territory of the facial nerve of a single hemiface. The differential diagnosis between these two entities, whose pathophysiological mechanisms are very different, can be made by electroneuromyographic (ENMG) examination. In addition, magnetic resonance imaging (MRI) is essential to show the offending vessel at the origin of pHFS and the absence of other causes of nerve compression. However, the diagnosis cannot be made on MRI basis alone, since a neurovascular conflict can be present in clinically asymptomatic subjects. This article reviews the clinical, MRI, and ENMG features in favour of a pHFS diagnosis as well as the various differential diagnoses of this involuntary facial movement disorder.