The study was based on 164 twin pairs from the older cohort of the Swedish twin registry. The main purpose of the study was to analyze previously recorded data concerning gingival bleeding in members of twin pairs with differing smoking exposure. Other periodontal disease factors analyzed were plaque index, alveolar bone index and tooth loss. It was found that the degree of alveolar bone loss and the number of teeth lost were greater in twins with a high life-time smoking exposure than in their twin partners with a low life-time exposure. Contrary to expectation, it was found that gingival bleeding propensity was less prevalent in the high exposure group. It is concluded that the validity of gingival bleeding as a sign and a symptom of inflammatory periodontal disease may be reduced as a consequence of smoking.