We wanted to test the hypothesis that gender differences in effects of smoking on the rate of decline in pulmonary function may be related to gender differences in the frequency of smoking. Data from the Vlagtwedde-Vlaardingen study in The Netherlands were analysed, to investigate the rate of decline in forced expiratory volume in one second (delta FEV1) in relation to smoking status and gender. 4,554 participants, initially aged 15-54 yrs, provided 16,900 pairs of observations at 3 yr intervals over 24 yrs of follow-up. Lifetime nonsmokers accounted for 11% of male participants and 45% of female participants. Compared with lifetime nonsmokers, estimated excess delta FEV1 for light, moderate, and heavy continued smokers was 4.4, 9.5 and 13.5 ml.yr-1 for men and 6.1, 10.8 and 18.8 ml.yr-1 for women, respectively. Female former smokers had a significantly more rapid delta FEV1 (beta = 4.4, SE = 1.6 ml.yr-1) than lifetime nonsmokers; but male former smokers had a slower rate of decline (beta = 4.1, SE = 2.3 ml.yr-1) than lifetime nonsmokers. Overall gender difference in smoking effects on delta FEV1 was statistically significant. Among subjects who smoked an identical amount at the beginning of the study period those who quit smoking during the period had a significantly slower delta FEV1 than those who continued smoking, for both men (beta = 20.6, SE = 3.9 ml.yr-1) and women (beta = 15.7, SE = 3.4 ml.yr-1). Younger quitters (< 45 yrs) benefited significantly more from smoking cessation than older quitters (> or = 45 yrs).(ABSTRACT TRUNCATED AT 250 WORDS)