Results of cryosurgical treatment in 102 patients with a histologically confirmed diagnosis of severe dysplasia or carcinoma in situ of the uterine cervix (CIN III) are presented. The colposcopic evaluation performed in all patients required full visualization of the squamocolumnar junction. In 95 of the 102 patients no significant cytological abnormalities were found during the follow-up period, which amounts to a success rate of 93%. In seven patients (7%) treatment was considered to have failed because cervical smears persistently suggested CIN II or III. In five of them this was in all probability due to a residual lesion, since the abnormal smears occurred within 12 weeks after cryosurgery. It is concluded that in selected cases cryosurgery is a safe alternative for conisation in the treatment of CIN III. However, thorough colposcopic expertise is essential for adequate preoperative screening, as is careful selection of patients, and the latter may result in the withholding of cryosurgical therapy from 30% of patients with CIN III.