A total of 204 infertile women attending the Infertility Clinic of the Medical Center Hospital of Vermont were studied for the possible role ofChlamydia trachomatis and intrauterine contraceptive device (IUCD) use as factors related to their infertility. All patients had had at least 1 year of involuntary infertility. All but one woman had negative cultures forC. trachomatis, but a highly significant correlation (p < 0.001) was evident between evidence of prior pelvic inflammatory disease (PPID) as documented by hysterosalpingograms and/or laparoscopy and the prevalence of chlamydial antibody. Furthermore, a significant (p = 0.01) correlation could be shown between the prevalence of the antibodies and adnexal adhesions. IUCD use could also be shown to correlate significantly (p < 0.001) with PPID, and a detailed statistical analysis indicated that the two factors, antibody toC. trachomatis and a history of IUCD use, were independently related to PPID. Only about one third of the patients with PPID could ever recall having had an illness consistent with PID. Subsequent to the infertility workup, 76 of these women became pregnant and there was a significant (p < 0.001) correlation between the occurrence of ectopic pregnancy and antibody toC. trachomatis. A significant (p = 0.01) correlation was also noted between a history of IUCD use and subsequent ectopic pregnancy. From these data it appears that antecedent infection withC. trachomatis, as measured by antibody prevalence, and a history of IUCD use are important factors in infertility of tubal origin and are also related to ectopic pregnancy.