BACKGROUND Defective sperm quality is a significant cause of infertility. It is known that cigarette smoking affects semen quality. Our aim was to compare the semen of infertile cigarette smokers with infertile non-smokers to study the effect of smoking on semen quality. METHODS Semen samples of 100 cigarette smokers and 100 strictly non-smoking primary infertility patients were included in the study, following stringent exclusion criteria. Smokers were categorised as light, moderate and heavy smokers. Semen samples were examined for asthenozoospermia, oligozoospermia and teratozoospermia, according to World Health Organisation guidelines. RESULTS 39 percent of non-smokers showed normozoospermia, while only three percent of smokers were normozoospermics. Light smokers predominantly showed asthenozoospermia. Heavy smokers showed asthenozoospermia, teratozoospermia and oligozoospermia. Statistical analysis using Fisher's exact test showed that the incidence of both isolated asthenozoospermia (p-value is 0.0015) and asthenozoospermia with teratozoospermia (p-value is 0.0106) among smokers was significant, in comparison to non-smokers. Overall impact of asthenozoospermia (p-value is less than 0.0001) and teratozoospermia (p-value is 0.0328) but not of oligozoospermia was observed on the semen quality in smokers, compared with non-smokers. CONCLUSIONS Asthenozoospermia, the most common semen variable in our study, can be an early indicator of reduction in quality of semen, as seen in light smokers. In addition, heavy smoking produces teratozoospermia, which further reduces semen quality. Oligozoospermia may be due to factors other than smoking.