Between 1965 and 1980 we performed 512 Shirodkar operations. Mean age of the patients was 28.4 years. The most frequent diagnosis was incompetence of the internal cervical os, which accounted for 74% of the operations, the remaining 26% being prophylactic. Sutures were performed between the 12th and the 18th week of gestation and 76.3% of these patients had normal births (mean gestation time 39 weeks). Without Shirodkar operations, out of 748 pregnancies studied, 23.1% resulted in normal birth; whilst with Shirodkar 90.5% of 462 pregnancies were successfully delivered at term.