Aim: To analyse the possible effect of seasonal variation on semen parameters. Methods: The participants consisted of 1688 men attending the andrology laboratory between 1991 and 1997 for reduced fertility in the couple. Semen analysis was performed according to the WHO manual. The 84 individual months of the study period were each assigned to one of the three groups according to the average monthly outside temperature; Group A (temperature <4.4℃), Group B (4.4℃-13.3℃) and Group C (>13.3℃). Results: When comparing the different sperm parameters, the morphology was significantly better in Group C. However, when the smokers were analysed separately, this difference disappeared and significant seasonal variations were found in sperm density, total sperm count, motility and total motile sperm; they were deteriorated in the warmer season. In non-smokers, no such negative effect of increased temperature was observed. Conclusion: Sperm quality is influenced by seasonal factors. Increased environmental tempe Aim: To analyze the possible effect of seasonal variation on semen parameters. Methods: The Groups consisted of 1688 men attending the andrology laboratory between 1991 and 1997 for reduced fertility in the couple. Semen analysis was performed according to the WHO manual. months of the study period were each assigned to one of the three groups according to the average monthly outside temperature; Group A (temperature <4.4 ° C), Group B (4.4 ° C-13.3 ° C) and Group C (> 13.3 ° C) When comparing the different sperm parameters, the morphology was significantly better in Group C. However, when the smokers were analytically separately, this difference disappeared and significant seasonal variations were found in sperm density, total sperm count, motility and total motile sperm; they were deteriorated in the warmer season. In non-smokers, no such negative effect of increased temperature was observed. Conclusion: Sperm quality is influenced by seasonal factors. Increa sed environmental tempe