It is emphasized that both metaplasia and CIN (cervical intra-epithelial neoplasia) must be defined with great precision in order to optimize an individualized treatment. In addition, if the metaplasia or CIN is classified as koilocytotic, the koilocytes must necessarily be found in the same cell layers as the metaplastic and/or the neoplastic cells. In a material of 335 unselected, consecutively treated women evaluated colposcopically, a marked difference between dysplasia (CIN 1 -2) and preinvasive cancer (CIN 3) was found cytologically and histologically, in that the incidence of koilocytotic atypia in CIN 3 lesions was only half of that in CIN 1 -2 lesions. The diagnostic accuracy of cervicovaginal cytology in koilocytotic metaplasia and koilocytotic CIN was poor: exfoliated koilocytotic cells were found in only 25% of the cases with histologically proven koilocytotic atypia, even when the cytological smears were reexamined. Furthermore, no characteristic colposcopic picture of koilocytotic metaplasia or CIN was found. It seems probable that koilocytotic dysplasia does not necessarily behave in the same way as classical CIN, which has been thought to progress continuously from mild dysplasia (CIN 1) to preinvasive cancer (CIN 3), since rapid progression of koilocytotic CIN 2 lesion directly into invasive cancer has been demonstrated. The C02-laser has been used to treat koilocytotic cervical intra-epithelial neoplasias. In 49 of the 52 cases so treated in this series, complete eradication of the disease was noted at two postoperative colposcopic and cytological examinations, 3 and 6 months after treatment, respectively.