The object of the study was to assess the incidence of lingual nerve sensory loss during removal of impacted mandibular third molar teeth, and the effect of retention of the lingual plate on the incidence. The subjects were 395 patients, of whom 362 completed the study. Removal of 504 impacted wisdom teeth with retention of the lingual plate was performed. Results showed that 381 (76%) of the teeth were partially erupted and the remaining 123 were unerupted. In 497 (99%) bone had to be removed, and of these 376 (76%) required division of the tooth before removal (75% of the entire series). The only complication was transient paraesthesia in one patient which settled within a month. The study concludes that retention of the lingual plate gives optimum protection to the lingual nerve during removal of impacted wisdom teeth.