Inconsistent results have been reported for the semen quality in HIV-infected men, due to the biases inherent in some studies. The objective of the present study was to investigate the semen parameters in HIV-1-infected patients and to compare their sperm characteristics with those of a control group of fertile, noninfected men. Factors implicated in semen alterations in HIV-1 patients were also analyzed. HIV-infected men (n=190), of whom 91% were undergoing antiretroviral therapy, and 218 fertile men were studied. Infertility risk factors were recorded and clinical examinations were performed for both groups. Records of history of HIV infection, antiretroviral treatment, and HIV-1 RNA detection in the blood as well as HIV-1 genome detection in the semen were obtained for the infected patients. Semen volumes, percentages of progressive motile spermatozoa, total sperm counts, and polymorphonuclear cell counts were decreased, while the pH values and spermatozoa multiple anomaly indices were increased in HIV-infected patients. Even after adjustment for possible sources of bias, the decreases in semen volume and progressive motility and the increase in pH remained significant. The present study demonstrates sperm motility and ejaculate volume alterations in HIV-1-infected patients, most of whom were receiving antiretroviral therapy. In HIV-1 patients, further longitudinal studies are required to analyze the impact of treatment regimen on sperm parameter alterations.