The present report assesses 15 years' experience with electrocoagulation diathermy in the treatment of cervical intraepithelial neoplasia (CIN). Selection is based on the ability to visualize the boundaries of the lesion colposcopically. Visualization, together with cytology and target biopsy, should exclude invasive carcinoma. Histologically confirmed CIN of varying severity (almost two thirds were CIN III) was treated by diathermy in 1864 patients. The size of the lesion varied, and at times the lesion extended into the endocervical canal. Cervical intraepithelial neoplasia was eradicated in 97.3% of patients by a single diathermy treatment. Ninety-three percent of all patients under the age of 30 with CIN were treated by this method. Progression to invasive carcinoma after diathermy has not been demonstrated. A single treatment with electrocoagulation diathermy has proved consistently to be the most effective superficial ablative method for primary eradication of CIN whether deep, extensive, or of major severity. (Obstet Gynecol 61:673, 1983)