We conducted a retrospective study on 201 conizations for CIN III done over the last 14 years. Of these, 53 (26.4%) had involvement of the margins, 114 (56.7%) had margins free of neoplasia, and 34 (16.9%) were not evaluated. Of the 53 cases with margin involvement, 28 (52.8%) had complementary surgery and 25 (47.2%) cytological follow-up. Residual CIN was identified in the surgical specimen in 15 cases (53.6%) and microinvasion was present in 2 cases (7.1%). Of the 114 patients with margins free of neoplasia in the cone, 12 had a hysterectomy during follow-up for CIN III diagnosed by cytology and biopsy. Seven of these 12 patients (58.3%) had CIN in the surgical specimen and none had microinvasive cancer.