The aims of this study were threefold: (1) to describe iatrogenic lesions to oral branches of the trigeminal nerve, signs and symptoms, and functional status, (2) to report on a simple neurosensory examination method, and (3) to discuss means of prevention of iatrogenic injury. The etiology and functional status of 449 injuries to oral branches collected over 18 years were retrospectively reviewed. A simple scheme of a clinical neurosensory examination was applied to enable a quantified rating of the perception. Injury to the lingual nerve (n = 261) is not only the most prevalent type of lesion, it also seems to be the most devastating type of lesion. Third molar surgery (n = 319) counts for the majority of injuries to the lingual, inferior alveolar, and buccal nerves. Lesions related to the injection of local analgesics was the second most frequent etiology (n = 78), and the lingual nerve was affected more frequently and severely than other oral branches of the trigeminal nerve. The female gender was overrepresented in incidence of injured nerves but no difference was found in the severity of affection between females and males. All grades of loss of neurosensory functions were found, and a range of neurogenic malfunctions was reported. Methodological obstacles in clinical neurosensory examination of trigeminal nerve injury and the magnitude of neurosensory impairment are discussed. Many nerve injuries are avoidable by critical reevaluation of indications, increased awareness of potential hazards, and modified surgical procedures.