The long-term effects on periodontal tissues of impacted lower 3rd molar surgery have been investigated in a retrospective study comprising 51 cases. The postoperative examinations took place 2 and 4 years after the surgical treatment and included both clinical and radiographic variables. Assessments were made regarding the oral hygiene status, gingival condition and periodontal tissue breakdown in terms of increased probing depths and intrabony defects. Comparing the results of the two examinations, no significant changes of the incidence of plaque and gingivitis were seen on the distal surface of the 2nd molar, nor any significant change concerning the probing depth. The proximal bone level distal to the second molar was recorded by radiographic examination with a cut-off periodontal probe as indicator. Two years postoperatively, 16.7% of the cases aged less than or equal to 25 years showed intrabony defects exceeding 4 mm, compared with 40.7% in the age group greater than or equal to 26 years. At the 4-year re-examination, the corresponding figures were 4.2% and 44.4%, respectively. The improvement concerning the alveolar bone level was mainly seen in individuals under 25 years. Some factors affecting the periodontal healing after impacted lower 3rd molar surgery are discussed.