Identified risk factors for ectopic pregnancy (prior pelvic inflammatory disease, smoking at the time of conception, intrauterine device, obstetrical and surgical history) explain from 60 to 65% of the cases. Egg anomalies may also be a risk factor as it is likely that the transport of an abnormal egg along the uterine tube is less efficient than a normal one. We tested this hypothesis with data from two case-control studies with the same design covering a total of 1955 women. The risk of ectopic pregnancy increased specifically with age, which is compatible with our hypothesis. We also studied the associations with spontaneous abortion, considered to be a marker of the risk of pregnancies involving chromosomal malformations. We observed an association between ectopic pregnancy and spontaneous abortions (especially recurrent abortions), not explained by other known risk factors. Although our data do not supply a single definitive demonstration, our results converge to suggest that egg chromosomal anomalies may play a part in ectopic pregnancy aetiology.