The obstetric performance of 50 consecutive women with minor müllerian anomalies was compared with that of 141 subjects having a normal uterine cavity on hysterosalpingography. All 191 patients had a history of some years' infertility. Spontaneous abortion was the outcome of the first pregnancy in 27.8% of women with müllerian anomalies (not statistically different from the outcome of the control group). However, the evidence of a greater risk of variously complicated first pregnancies and labors (30.3% versus 12.9%, p less than 0.05) and of emergency cesarean sections (21.2% versus 7.1%, p less than 0.05) in the group of minor müllerian anomalies than in the group with normal uteri confirmed the innate pathologic condition and clinical significance of these mild to moderate malformations present in about 40% to 50% of oligomenorrheic women. The most frequent complications were threatened abortion and abnormal fetal lie. Even the very mildest müllerian anomalies seemed to have gynecologic and obstetric implications, but the clinical impact in this group still remains uncertain. It is concluded that a genital tract anomaly of a certain obstetric significance (ratio between distance from nadir of fundal indentation to line connecting summits of uterine horns and length of this line or H/L ratio greater than 0.15) must be suspected in about one third of women with oligomenorrhea. Consequently a high risk in the event of a future pregnancy is evident, and about half the pregnancies (42.1%) in this group will be complicated in one or more ways.