Objective: To study the relation between recurrent pregnancy loss (RPL) and infection with Chlamydia trachomatis, and to compare the prevalence of antibodies to C. trachomatis in women with primary and secondary RPL. Design: Prospective comparative study. Setting: University hospital and university student health center. Patient(s): Seventy patients with RPL were selected from women attending an RPL outpatient clinic; 40 normal parous women and 94 asymptomatic sexually active women served as controls. Intervention(s): Blood samples were collected during the clinical examinations for RPL. Main Outcome Measure(s): Serum immunoglobulin (Ig) G and IgA antibodies were detected by two independent methods, a recombinant ELISA specific to the genus Chlamydia and microimmunofluorescence testing specific to the species C. trachomatis. Result(s): There was no statistically significant difference in the frequencies of IgG or IgA between the women with RPL and the controls. The antibody frequencies were similar in the women with primary and secondary RPL. Conclusion(s): The presence of serum antibodies to C. trachomatis is not associated with RPL. Women with primary and secondary RPL do not differ with respect to the prevalence of antichlamydial antibodies. Thus, women with RPL do not benefit from screening for chlamydial IgG or IgA antibodies.