OBJECTIVE To evaluate the incidence of chromosomal abnormalities in ectopic pregnancy chorionic villi. METHODS A prospective study of patients with the diagnosis of ectopic pregnancy was conducted, with chorionic villi obtained at the time of surgical therapy cultured and analyzed for karyotype. Review of the patient's medical record and ultrasound evaluation was then completed and findings correlated with karyotype results. RESULTS Twenty-two patients undergoing surgery for the diagnosis of ectopic pregnancy yielded chorionic villi for culture. Successful culture was performed in 21 patients, with 3 (14%) revealing abnormal karyotypes. Review of the medical record showed ultrasound results consistent with fetal development or a gestational sac in 15 of 18 patients with normal chromosomal analysis. Three of 6 patients without fetal development yielded abnormal chromosomal findings. CONCLUSIONS Our results confirm that a high degree of success can be achieved in the karyotype analysis of ectopic pregnancy chorionic villi and that these conceptuses have a rate of abnormality similar to that reported for intrauterine gestations. Our data further suggest that when a gestational sac or fetal pole is identified by ultrasound, there is usually a normal karyotype.