摘要Objectives To study the association between cigarette smoking and sperm densityin men of reproductive age. Methods We enrolled 224 male employees of a modern petrochemicalplant in Nanjing,China. These men had no prior history of infertility or other reproductive diseases.Epidemiologic data, including information on smoking and other occupational and lifestyle exposures wereobtained by a questionnaire interview. Semen specimens were collected from each participant and analyzedaccording to the WHO guidelines. Regression analyses were performed to estimate the effect of smokingon sperm density. Results Approximately 67% of the subjects had ever smoked cigarettes. Differ-ent measurements of smoking behavior were each associated with decrensed sperm density. There was asignificant dose-response trend between the tertiles of total smoking amount in pack-years and sperm den-sity. As compared to men who never smoked, current smokers had a significant reduction in sperm densi-ty (-13.3×106/ml; 95% CI,-24. 1,-2.5) ,while ex-snokers had only a small decrement inspern density (-2.6× 106/al; 95 % CI,-18. 7 ,13. 5). Starting smoking at less than 20 yearsof age was associated with significant reduction in sperm density (-14.8×106/md; 95% CI ,- 27. 4, - 2.2). Starting smoking at 20 years or older was associated with a slightly snaller de-crease (-10.1×106/ml; 95% CI,-21.7,1.4). Conclusions Cigarette smoking is associ-ated with decreased sperm density ,showing an evident dose-response trend in this population.