CONTEXT AND OBJECTIVE: In cases of peripheral facial paralysis (PFP), diminished facial movements and their resultant cosmetic sequelae may have significant emotional repercussions, in addition to producing pronounced functional deficits. Abnormal muscle proprioception and deviation of the nasal-labial filter may also interfere with articulation of the labiodental and bilabial phonemes, thus diminishing speech intelligibility. In relation to stomatognathic functions, weakened labial occlusion decreases intraoral pressure, thereby hindering liquid retention in the buccal cavity and giving rise to vestibular stasis on the paralyzed side. The aim of this study was to evaluate the reliability of the labial commissure angle (LCA) as an anthropometric marker for objectively assessing changes in facial muscle tonus.