Colposcopy plays an essential role in the diagnosis and treatment of dysplasias of the uterine cervix. It may be used to assess the lesions recognising dysplasia, observing the degree of severity and indicating regions from which biopsies should be taken. It accurately defines the limits of the lesions by indicating the site of the squamo-columnar junction, on the ectocervix or in the cervical canal. In association with Schiller's test, it defines the peripheral limits of the lesions on the cervix or vagina and leads to the discovery of purely vaginal lesions. On the basis of such an assessment, it is possible to discuss appropriate method for reaching a histological diagnosis, perform selective biopsies or obtain surgical specimen, and the best form of treatment. Only colposcopy offers the possibility of determining the indications for local treatment and observing patients after treatment. Colposcopy must be accompanied by precise technique in the histological examination of biopsies and operative specimens. Colposcopy is not a routine method of examination. In order to be effective and reliable, it must be selective and performed by a specialised colposcopist.