Colposcopy was performed in 91 women who had cervical cytology suggesting mild dyskaryosis or showing koilocytosis, all previous cytology having been normal. The final histological diagnosis was CIN III in 22%, CIN II in 18%, CIN I in 31%, koilocytosis alone in 14% and no abnormality in 15%. These results indicate that even with mild cytological atypia, a high proportion of patients will have more advanced disease when colposcopy-directed punch biopsy is performed.