A total of 1628 women with CIN 3 treated with the Semm cold coagulator between 1975 and 1989 was followed primarily by cytology. The standard suitability criteria for ablation were adhered to except that patients were treated at their first visit when the colposcopist expected that the diagnosis would be no worse than CIN 3. Overall 97% of the women were treated at their first visit. In 30 women (2%) the histology was glandular or worse than expected, but 22 of these showed no persistent cervical disease subsequently. Follow-up was achieved for 87% at 10 years. In actuarial terms the primary success rate was 95% at 1 year and 92% at 5 years, it was similar for all age groups. Repeat cold-coagulation for persistent/recurrent CIN 3 was less successful and is not advised. The outcome for 226 pregnancies established after treatment is known. The rates for miscarriage, preterm or operative delivery were not increased. Cold-coagulation of CIN 3 at 100 degrees C as performed by us is as effective as any other treatment and calls into question the need for more expensive practices.