The aim of the present study was to determine whether there were significant monthly variations in the semen parameters (i.e. volume, sperm count, total sperm count, motile and normal sperm count) of men living in a Mediterranean climate area. A total of 10 877 semen analysis results were included. Semen samples were obtained as a part of an initial screening of male partners from couples with infertility problems who were attending our laboratory from 1970 to 2000. Log transformation and cubic root transformation were used to test the sample distribution. Statistical significance was adjusted by year of examination, patient's age and sexual abstinence period by performing covariance analyses. Differences between months were assessed with the Bonferroni post-hoc test. There was an increase in March and a decrease in September in the adjusted mean sperm count (p < 0.0005), total sperm count (p < 0.0005), motile sperm count (p=0.01) and normal sperm count (p=0.002). There were no variations in semen volume in the study period. Monthly changes in semen quality are confirmed in this population.