To assess the chromosomal aberrations in the abortus in recurrent miscarriage and the live birth rate after a euploid or aneuploid miscarriage.Retrospective analysis.Tertiary referral unit in university hospital.One hundred sixty-seven patients with 3 to 16 miscarriages before 20 weeks.Material collected at curettage from 167 abortuses was analyzed by standard G-banding techniques.The incidence of aberrations and the outcome of the subsequent pregnancy were assessed according to the embryonic karyotype.In this study 125 specimens were successfully karyotyped. Of these, 29% (36 of 125) had chromosome aberrations; 94% of the aberrations were aneuploidy, and 6% were structural. The most prevalent anomalies were chromosome 16, 18, and 21 trisomies, triploidy, and monosomy X. After an aneuploid miscarriage, there was a 68% subsequent live birth rate (13 of 19) compared to the 41% (16 of 39) rate after a euploid abortion.The low (29%) incidence of aberrations indicates that alternative mechanisms may be responsible for the majority of recurrent miscarriages. These figures provide a basis for assessing the efficacy of therapy for recurrent miscarriage. If further studies confirm that patients with karyotypically abnormal fetuses have a good prognosis, an informed decision can be made as to whether further investigations and treatment should be undertaken.