Effects of cigarette smoking and smoking cessation on rate of FEV1 decline over 6 yr were examined in 4,451 Japanese-American men from the Honolulu Heart Program who were 45 to 68 yr of age at baseline (1965-1968). Within-person regression was used to calculate annual change in FEV1. Rates of FEV1 decline varied strongly with smoking status and increased significantly with age. Overall, men who continued to smoke experienced steeper rates of decline compared with men who never smoked (-33 ml/yr versus -22 ml/yr, respectively; p = 0.0001). Rates of decline for those who quit smoking during the first 2 yr (-32 ml/yr) were nearly the same as those who continued smoking (-34 ml/yr). After quitting, their rates of decline diminished to a level (-19 ml/yr) similar to that of men who had never smoked (-21 ml/yr). FEV1 decline in continuing smokers was significantly associated with duration of smoking, whereas associations with intensity and pack-years were of borderline significance. Among 216 men with impaired pulmonary function, those who quit smoking had significantly slower rates of FEV1 decline than did those who continued smoking. Potential reasons for quitting included respiratory conditions and stroke. These results extend previous reports of accelerated rates of FEV1 decline in the persons who continue to smoke, and they indicate that smoking cessation leads to less steep rates of decline in pulmonary function over a short period of time in middle-aged men, as well as in men with established pulmonary impairment.