As a good number of couples are coming to infertility clinics to have children at advanced ages, it is essential to know whether advanced paternal age is associated with diminished semen quality and a higher risk of infertility. This retrospective study was done to see the effects of age on semen quality, a well-known indicator of fertility status. Semen parameters of smokers and non-smokers in the study population were also analyzed. A sample of 1121 male partners of infertile couples (aged 25-55 years) who came to an infertility clinic for treatment were included into the study. In addition to clinical history including lifestyle, medical and occupational details and physical examination, their semen samples were examined. Semen volume (ml), sperm concentration (x 10(6)/ml), motility (%), rapidly progressing (%), slowly progressing (%), non-progressive (%) motility and morphology (%) were measured. Semen volume showed IQR 1.5-3.0 ml, and significant decreasing trend with increasing age (r = -0.070, p<0.05). Sperm motility and rapidly progressing motility showed significant decrease (IQR 40.0-70.0, r = -0.115, p<0.01 and IQR 20.0-50.0, r = -0.107, p<0.01 respectively) with increasing age. There was no significant difference between semen parameters of smokers and non-smokers in the study population. This study shown that semen volume, sperm motility and rapidly progressing motility were significantly decreased with increasing age.