We prospectively studied 2140 clinically healthy men to assess the influence of smoking on longitudinal decline in one-second forced expiratory volume (FEV1.0). All the subjects had annual medical checks including pulmonary function tests from 1995 to 1999. The mean values +/- standard deviations of annual decreases in FEV1.0 (slope) were 22 +/- 49 mL/year in non-smokers, 26 +/- 52 mL/year in former smokers, and 33 +/- 57 mL/year in current smokers (p < 0.01; non-smokers vs. current smokers). The adjusted slope (slope divided by predicted value of FEV1.0, per year) in current smokers was also greater than that in non-smokers (p < 0.01). Multiple regression analysis revealed that initial age, height, FEV1.0, and smoking status were significant parameters for determining the slope. This study clearly showed that smoking is an important risk factor foracceleration of the aging-related longitudinal decline in pulmonary function in Japanese men.