Objective To determine whether frozen section in conisation improves the management of cervical intraepithelial neoplasia.

Design Randomised trial.

Setting Department of Obstetrics and Gynaecology, Conception Hospital, Marseille, France.

Population Patients referred for treatment or diagnosis of cervical intraepithelial neoplasia.

Methods Two hundred and three patients requiring conisation for diagnosis or treatment of cervical pathology were randomly assigned to have (n= 102) or not (n= 101) a frozen section of the endocervical margin of the cone specimen.

Main outcome measures The principal criterion was the 12 month residual or recurrent high grade disease rate.

Results At 12 months, the residual or recurrent disease rate of high grade lesions was 12.6% in the group that did not have frozen sections and 1% in the group that did (relative risk, RR, 11.9, 95% CI 1.6–89.5, P= 0.0025). The corresponding rates of margin involvement were 18.9% and 1%, respectively (RR 15.13, 95% CI 2.06–111.27, P= 0.0002). The groups did not differ as to the height of the cone (13.6 [5.6] mm vs 13.7 [4.7] mm, P= 0.75) or post-operative morbidity (6% vs 7%, RR 1.01, 95% CI 0.94–1.09, P= 0.8). The rate of patients lost to follow up was similar in both groups 17% vs 12% (RR 1.42, 95% CI 0.71–2.81, P= 0.31).

Conclusion Frozen section is effective in conisation and significantly reduces residual or recurrent high grade disease. This finding improves the management of cervical pathology achieving immediate clear margins in most of conisations. This is of great interest because high rates of patients are lost to follow up as we and others authors have found.