Diplopia caused by local anesthesia at the superior posterior alveolar nerve for the removal of the maxillary third molar is a rare complication. The diplopia is due to facial palsy of the oculomotor muscles of the globe. This paper describes the case of a 22-year-old woman, in whom diplopia was observed after an overall uncomplicated removal of the semi-impacted third molar. Possible causes of the anesthetic effects are reported. The most accepted explanation is that the anesthetic diffuses on the abducent nerve in the cavernous sinus. The necessary actions that the dental surgeon must perform are reported.