The aim of the present study was to confirm the seropositive rate of Helicobacter pylori to which antibodies cross-react with spermatozoon flagella in patients with infertility. Of the 204 patients in whom the anti-H. pylori IgG antibody in serum and follicular fluids were measured, 45 (22.1%) were seropositive for H. pylori and the seropositive percentage of infertile patients without any possible cause was higher than that of patients with one or more known infertility factors [8 of 21 patients (38.3%) vs. 37 of 183 patients (20.2%), respectively], which suggests a new concept: H. pylori-related infertility.