In this study, we investigated the prevalence of Ureaplasma urealyticum and Mycoplasma hominis infection among 250 unselected infertile men, the presence of urogenital symptoms in infected men and the effects of these microorganisms on the conventional sperm parameters. Urethral samples were obtained using a swab inserted 3-4 cm into the urethral meatus. Ureaplasma urealyticum and Mycoplasma hominis were detected by the kit Mycofast R evolution 3 Elitech Microbiology (Elitech Microbiology, Signes, France). Ureaplasma urealyticum was detected in 15.6% of the cases and Mycoplasma hominis in 3.6%. One patients had a co-infection with both pathogens. About 41% of the infertile patients with mycoplasma infection had urogenital symptoms. A lower number of patients with mycoplasma infection had normal sperm parameters compared with non-infected infertile men, but this frequency showed only a trend compared to non-infected patients (Chi-square=3.61; P=0.057), and a significantly higher percentage of patients with oligo-astheno-teratozoospermia (Chi-square=127.3; P<0.0001), or asthenozoospermia alone (Chi-square=5.74; P<0.05) compared to non-infected infertile patients. In conclusion, this study showed an elevated prevalence of Ureaplasma urealyticum and Mycoplasma hominis infection in unselected men attending an infertility outpatient clinic and that the presence of these microorganisms is associated with a higher percentage of patients with abnormal sperm parameters.