Objectives Although the harmful effects of smoking on periodontal disease and oral cancer are now indisputable, its effect on dental caries is less well known. This study assessed whether daily smoking predicts caries increment in adults over 4 years. Methods Data from 955 adults who participated in both the Health 2000 Survey and the Follow-Up Study of Finnish Adults' Oral Health were analysed. At baseline, participants provided information on demographic characteristics, education and dental behaviours. The 4-year net increment in the numbers of decayed (DT), filled (FT) and missing (MT) teeth and the DMFT index were calculated using the data from baseline and follow-up clinical oral examinations. Results Daily smoking was not associated with net DMFT increment. In subsequent analysis by components, daily smoking was associated with net DT increment, but not with net FT or MT increments. When daily smokers were split into two groups by consumption level (1-19 and 20+ cigarettes/day) and compared to nondaily smokers, a significant dose-response relationship was additionally found between levels of tobacco consumption and net DT increment. Although daily smokers reported less favourable behaviours than nonsmokers, these associations only explained partially the effect of daily smoking on net DT increment. Conclusions Daily smoking was independently related to caries development (net DT increment) in adults over 4 years, but not to caries treatment (net FT and MT increments) or caries experience (net DMFT increment).