Tobacco smoking is a factor claimed to be of influence on alveolar bone loss. The purpose of the present study was to investigate whether the effect of changed smoking habits is associated with the progress of proximal marginal alveolar bone loss as measured on intraoral radiographs. The study comprised 349 individuals with twenty or more remaining teeth examined in 1970 and 1980. The bone loss in the period was measured as the difference in the ratios "bone height/root length" at proximal tooth sides between the two examinations. It was found that the marginal bone loss in "Non smokers in 1970 and 1980" was as a mean 3.9 per cent of the root length. The corresponding value among "Smokers 1970 and 1980" was 6.0 per cent. The difference is statistically significant (p = 0.001). In individuals who had given up smoking during the 10-year period (bone loss: 4.4 per cent) as compared with those who had smoked regularly, the progression of bone loss was significantly (p