This retrospective study was to analyze the inferior alveolar nerve and lingual nerve damage after the removal of mandibular third molars. In this questionnaire study, the subjects chosen for this study were 2472 dentists who answered the questionnaire about numbness after the extraction of lower third molars. The data collected by E-mail and web site included the incidence of removal of the lower third molars, the incidence and the experience of numbness of the inferior alveolar nerve and lingual nerve, rate and duration of recovery, the influence in day life after the long-term sensory loss, the period and amount of the indemnity in the case of medical dispute. The results are summarized as follows. 1. The experience rate and the incidence rate of the inferior alveolar nerve numbness by oral surgeons in the past year were19.9% and 0.14%. Those of the lingual nerve by oral surgeon were 7.7% and 0.05%.2. The experience rate and the incidence rate of the inferior alveolar nerve numbness by the dentists except oral surgeons in the past year were 9.7% and 0.19%. Those of the lingual nerve by the dentists except oral surgeons were 5.5% and 0.11%.3. The recovery rate of the inferior alveolar nerve after 1 year and 2 years were 85.6% and 91.3%. The recovery rate of the lingual nerve after 1 year and 2 years were 84.8% and 89.3%.In conclusion, most of numbness may be recovered within 2 years. However the possibility of long term and persistent numbness should not be neglected. Therefore practitioner must inform the possibility of nerve injury and include this possibility in the consent forms.