A retrospective longitudinal review identified 341 women who had had a hysterectomy in association with CIN 3, in Tayside Region, during the years 1967-1977; 219 (64%) had completed 10 years of cytology follow-up and of 140 women eligible for 15-year smears 79 (56%) completed the 15-year follow-up. Eight (4%) of the 219 patients developed abnormal cytology, but in six, smears reverted to normal spontaneously. Two patients had persistently abnormal smears and vaginal intraepithelial neoplasia (VAIN) was diagnosed. Only one patient completing 15-year follow-up had an abnormal smear and VAIN later diagnosed. No patient over this 15-year period developed invasive vaginal carcinoma. Sixty vaginal carcinomas were identified during the period 1957-1987 from the gynaecology cancer register; only one was associated with a previous diagnosis of CIN 3 at hysterectomy. With such data we would propose screening 6-monthly during the first post-operative year and then at 2 years. If these smears were normal, the patient could then revert to the normal screening programme.