Harm reduction for continuing smokers has been suggested as a public health priority. We evaluated whether tobacco control programs might reduce cigarette consumption among current smokers through strategies aimed primarily at protecting nonsmokers from secondhand smoke (SHS). Data were from adult (18+ years) respondents to multiple (1990, 1992, 1996, 1999), large, cross-sectional, population-based surveys of smoking behavior, conducted to evaluate the California Tobacco Control Program. Adult daily smoking prevalence decreased from 15.9 +/-0.4%(+/-95% confidence interval) of the California adult population in 1990 to 13.0 +/-0.3% in 1999. Concurrently, moderate-to-heavy daily smoking (>or= 15 cigarettes/day) decreased from 10.3 +/-0.4% in 1990 to 7.4 +/-0.3% in 1999, and heavy daily smoking (>or= 25 cigarettes/day) from 3.4 +/- 0.2% in 1990 to 1.9 +/- 0.1% in 1999. Decreased daily smoking was observed in all demographic subgroups except young adults. Among college graduates, the daily smoking prevalence in 1999 was 6.4 +/- 0.4%, a level previously observed only among U.S. physicians. In 1999, nearly 30% of current smokers did not smoke daily, and more than 60% said they now smoked less than previously. In 1999, self-reported cigarette consumption was inversely related to believing SHS is harmful to nonsmokers, having a smoke-free workplace, and living in a smoke-free home. In California, tobacco control strategies that educated the population about SHS and resulted in smoking restrictions may have led continuing smokers to smoke less, which should reduce the harm from smoking to the public health in the long term.