ABSTRACT Aims The first prospective investigation of the extent to which parentalsmoking cessation predicts their children's daily smoking. Design Parental smoking status was assessed when children were aged8/9 years and children's smoking status was assessedat age 17/18 years. Setting Twenty Washington State school districts in the control groupof the Hutchinson Smoking Prevention Project. Participants and measurements Questionnaire data were gathered on 3012 children (49% femaleand 91% Caucasian) and both of their parents in a cohort witha 95% retention rate. Findings When both parents quit smoking, children's odds of dailysmoking were reduced by 39% (95% CI = 15%,56%) compared to when both parents were current smokers.Furthermore, when both parents never smoked then children’sodds of daily smoking were reduced by 71% (95% CI = 62%,78%). Conclusions Parental smoking cessation is associated with reduced risk oftheir children's daily smoking. Parents who quit stillplace children at substantially higher risk compared to parentswho never smoked. [ABSTRACT FROM AUTHOR]