THE OBJECT. Delimiting the place of hysterectomy in cases of lower genital tract intraepithelial neoplasias in women. LOCATION. The laser and colposcopy centre (CCL) of a maternity unit in Lausanne in the Vaudois University Hospital Centre (CHUV). THE TYPE OF STUDY. Retrospective on 1,303 patients between 1986 and 1990. THE SUBJECTS AND TREATMENT. 853 cases of cervical intraepithelial neoplasia (CIN) and 79 cases of vaginal intraepithelial neoplasia (VAIN) were treated with CO2 laser. The situations in which hysterectomy could be considered in the course of treatment are discussed. They are: 1) Dysplasia persisting after treatment, 2) when pathological tissue is found on examining slides from conisation specimens, 3) micro-invasive carcinoma, 4) post-operative obstructive stenosis. PRINCIPLE RESULTS. The multiple location of dysplasia lesions of the lower genital tract was calculated for all the patients examined. It shows that hysterectomy itself will be insufficient to remove all dysplasias since frequently (9.2%) of lesions are found in the vagina in cases that have dysplasia of the cervix. Residual lesions after hysterectomy are shown up by VAIN which are responsible for the persistence of changes in the control smears (in which there were 9 cases of VAIN3 after hysterectomy in this series). Treatment therefore is hazardous and only poorly successful because the site of these lesions is often hidden in the scar through the top of the vagina. Furthermore their discovery in uncertain since there is a tendency at present to avoid out cytological screening of these patients once they have undergone hysterectomy. CONCLUSION. The high incidence of multifocal lesions and the possibility that is very real of residual dysplasia after hysterectomy has made the authors limit the place of hysterectomy in these cases, preferring to use conservative treatments and emphasizing the need to continue cytological controls for after treatment.