The purpose of this prospective study was to evaluate the incidence of various complications, including alveolitis, infection and paresthesia of the inferior alveolar nerve, in association with removal of impacted mandibular third molars. The relation between these 3 complications and several clinical variables (age, sex, degree of impaction, surgical difficulty and use of oral contraceptives) was also examined. Data were collected prospectively for all patients who underwent extraction of an impacted third molar in a single private dental practice over a 12-month period. A variety of data were collected for each patient, including age, sex, medical status at the time of the procedure and type of procedure performed. Patients were contacted at 2 days and 4 weeks after surgery to establish the occurrence of complications, and those with complications were treated; those with paresthesia were followed for at least 24 months. A total of 550 impacted mandibular third molars were extracted from 327 patients (136 males and 191 females). The complication rate was 6.9%, consisting of 20 cases of alveolitis, 12 cases of infection and 6 cases of paresthesia of the inferior alveolar nerve. Of the 6 neurosensory deficits, 3 resolved and 3 were permanent. The risk factors associated with permanent neurosensory deficit were female sex, Pell and Gregory IC or IIC classification of impaction, and age greater than 24 years. The risk of postoperative alveolitis and infection was also greater among women. There was no significant relation between the use of oral contraceptives and alveolitis. Surgical removal of impacted mandibular third molars should be carried out well before the age of 24 years, especially for female patients. Older patients are at greater risk of postoperative complications and permanent sequelae. A surgeon's lack of experience could also be a major factor in the development of postoperative complications.