Infection related infertility is common in Nigeria. The study was designed to evaluate the involvement of sexually transmitted diseases (STDs) in the pathogenesis of male infertility. One hundred and eighty-two male subjects aged 18-56 years were investigated-fertile (85), infertile (50), men with STDs (47). Semen was analysed according to WHO guidelines and appropriate statistical tests performed. Over 65% of subjects with STDs had gonorrhea and non-specific urethritis(NSU). More than two-thirds of STDs subjects (76.4%) were dyspermic and oligospermia was most frequently observed in infertile subjects (30%). Sperm count, percentage motility and morphology were significantly lower in infertile than fertile controls (P<0.001) while percentage motility was significantly lower in men with STDs than fertile controls (P = 0.005). Gonorrhea and NSU are still prevalent in the Nigerian society. STDs may cause infertility in the African male by reducing sperm motility and semen volume