In Western culture, smoking is regconized as a factor which increases the rate of pseudarthrosis. However, in Japan we have only a few reports on the relationship between bone union and smoking. We report the effects of smoking upon lumbar posterolateral fusion. 49 patients underwent surgery from July 1996 to March 2000. The mean age was 48.2 years. 34 patients were male and 15 were female. 24 patients were smokers and 25 patients were nonsmokers. We observed their smoking habits and evaluated bone union on radiographs. 29.2% of the smokers developed pseudarthrosis, whereas the rate was 8.0% among the nonsmokers. In cases with instrument, 16.7% of the smokers had developed pseudarthrosis, whereas the rate was 0% among the nonsmokers. Smoking has adverse effect on bone union of lumbar posterolateral fusion.