The impact of quitting smoking on symptoms of chronic bronchitis: results of the Scottish Heart Health Study. Scotland has high rates of death from diseases of the respiratory system and high rates of smoking, especially among women. Data on self reported smoking and prevalence of chronic cough and chronic phlegm among 10,359 men and women aged 40-59 years were obtained from the Scottish Heart Health Study. Overall, current cigarette smokers had rates of chronic cough and chronic phlegm four to five times those of never smokers after standardisation for age (32.3% v 6.5% for men and 24% v 5.5% for women for chronic cough; 31% v 8.3% for men and 21% v 5.5% for women for chronic phlegm). Ex-smokers' symptom rates were a little above those of never smokers and were significant for chronic cough among women and chronic phlegm among men. Men had higher symptom rates than women and this was true for smokers, ex-smokers, and never smokers. The higher rates among men could not be explained by higher cotinine concentrations. Tests to detect "deceivers" among ex-smokers and never smokers using biochemical validation suggested that 87 (1.5%) respondents were in fact smoking; they were excluded from analyses. There were substantially lower rates of chronic cough and chronic phlegm within a year of stopping smoking, and two to four years after stopping 89-99% of the difference between current smokers and never smokers was accounted for (99% and 93% for men and women with chronic cough, 96% and 89% for men and women with chronic phlegm). Even 10 years after stopping, rates of symptoms among ex-smokers remained a little above those of never smokers (except for women with chronic phlegm), though these differences were not statistically significant. Former heavy smokers continued to have rates of chronic cough and chronic phlegm that were higher than those of former light and moderate smokers (though not significantly so). These are cross sectional data, but they emphasise the importance for chronic bronchitis symptoms of giving up cigarette smoking, though the amount previously smoked continues to exert a small influence. 