In a group of 316 conizations performed from January 1984 to July 1991, 68 patients (22%) revealed no free margins of cervical intraepithelial neoplasia (CIN). They were divided into two groups with: ‘negative follow-up’ [normal cytology or less than two smears suggesting CIN I (class IIIa)] and ‘positive follow-up’ [at least two smears suggesting CIN I or one smear suggesting CIN II (class IIIb) or worse]. Forty-five patients (66%) fulfilled the criteria of negative follow-up. All patients with CIN I at the cone margin (18) were found in this group. The other 23 patients were in the positive follow-up group. Patients with positive follow-up were significantly younger (p = 0.04). Intervention after incomplete cone biopsy was necessary in approximately 10% (7/68) of cases. Cytology was thereby a reliable indicator for residual disease. Higher grade of CIN involved at the cone margin predicted a higher chance of positive follow-up. Semiquantitative measurement of CIN in the cone specimen showed a severe involvement of CIN II and CIN III in the positive follow-up group. In sum, our study showed that CIN I at the margin of the cone biopsy has no clinical significance. However, CIN II or III at the margin needs a careful cytologic follow-up, and appropriate action should be taken in case of cytologic abnorm