Of 4,782 women attending a colposcopy clinic from 1964 to 1971, 4,358 were included in a prevention program for cervical cancer and were followed for at least ten years. Of them, 1,105 were untreated and 3,253 treated. One hundred two underwent surgery and 3,151, electrocautery (ECT). On the basis of the post-ECT colposcopic examination, cervices were divided into iodine dark and iodine light. One cervical intraepithelial neoplasia (CIN III) and three invasive cancers were found among the untreated women. Three neoplasias (one adenocarcinoma, one in situ carcinoma and one invasive carcinoma) were found among the treated non-CIN women, only one carcinoma among the treated CIN women and no neoplasias among the surgically treated women. The comparison showed a difference in favor of the treated group, though it was not statistically significant. A comparison between the observed and expected data on the basis of the literature was highly significant: the expected appeared high. While these data do not prove the basic hypothesis that ECT has a protective effect in cancer prevention, they do provide some evidence in favor of it.