This retrospective longitudinal study was undertaken in order to determine the incidence and reproductive impact of uterine malformations on women desiring to conceive during their reproductive years. A total of 3181 patients in whom the morphology of the uterus was ascertained by hysterosalpingography (HSG) and laparoscopy/laparotomy during the years 1980-1995 was included in the study. The population analysed included fertile, infertile and sterile patients. The overall frequency of uterine malformations was 4.0%. Infertile patients (6.3%) had a significantly (P < 0.05) higher incidence of Müllerian anomalies, in comparison with fertile (3.8%) and sterile (2.4%) women. Septate (33.6%) and arcuate (32.8%) uteri were the most common malformations observed. Each malformation was individually analysed in fertile and infertile patients, in order to ascertain its actual reproductive impact. The performance of the unicornuate and didelphys uteri was similar with a chance of having a living child of 37-40%. The reproductive potential of the bicornuate uterus showed a live birth rate of 62.5% and the septate uterus showed a live birth rate of 62%. In all these abnormalities, early miscarriages (25-38%) and preterm deliveries (25-47%) were quite common. The arcuate uterus presented a live birth rate of 82.7%. It is concluded that uterine anomalies are relatively frequent in fertile women, and more frequent in infertile patients. Nevertheless, fertile patients with normal reproductive performance do exist, and Müllerian defects can permit an absolutely normal obstetric outcome. The reproductive performance of the unicornuate and didelphys uteri was poor, while that of the septate and bicornuate uteri was better than expected. The arcuate uterus had no impact on reproduction.