The outcome of 635 pregnancies in 197 women before and after conization is reported. After conization a significant increase in premature deliveries occurred in young women (age 21-25), nulliparae representing the highest risk. The rate of premature deliveries in this age group was 4.4% before conization and 30.6% after conization. No such increase could be found in any other age group. Labor was notably short in non-parous women and in parous women it started with rupture of the membranes significantly more often after conization. In addition, a significant increase in the frequency of cervical stenosis was observed, but this was of clinical significance in only one case. Treatment in the form of prophylactic cerclage did not reduce the incidence of either premature delivery or of late spontaneous abortion.