During a 12 month period, tissue was collected from 30 surgically managed patients presenting with vital ectopic pregnancies. Chorionic villi of the removed tissue were successfully karyotyped by (semi-) direct chromosome technique in 22 cases. Only one abnormal chromosomal complement, a triploidy (69,XXX) was found. As controls, 10 cases of intrauterine pregnancies were investigated, all showing a normal karyotype. These findings do not suggest an important role for chromosome abnormalities in the aetiology of vital ectopic pregnancies.