Facial nerve palsy may occur in rare cases in connection with dental treatment. Its causes have not been entirely clarified so far. If facial nerve palsy sets in immediately after the administration of a local anesthetic, it is likely that the unintended, accidental anesthesia of the branches of the facial nerve has occurred. Once the effect of the anesthetic subsides, the palsy disappears and is completely reversible. Direct damage to the facial nerve with the injection needle seems improbable. Delayed facial nerve palsy, which ini-tially sets in hours or days after dental treatment, must be considered separately. In the past, various causes have been discussed in literature. Presently, it is thought that the most likely cause is the reactivation of viruses (herpes simplex virus type 1 or varicella zoster virus) from nerve ganglia of the facial nerve by dental treatment. This can also occur in cases where no local anesthesia has been used. In addition, this does not have to result in the formation of blisters on the skin (zoster sine herpete), which is typical of herpes labialis or herpes zoster. In order to treat delayed onset facial palsy after dental treatment, drug therapy with glucocorticoids (prednisolone) and antivirals (acyclovir) is the current recommendation. For successful therapy, the drugs should be administered in less than 72 hours after the onset of the first symptoms. Dentists should thus promptly refer patients to a neurologist and otherwise be aware of the potential (irreversible) damage to the facial nerve by the viruses. Palabras clave: Bell's Palsy, Treatment complications, dental treatment, facial nerve palsy, local anesthesia, viral infection