Large loop excision of the transformation zone (LLETZ) allows complete histologic assessment of cervical neoplasia. However, selective colposcopically directed punch biopsy followed by local ablation allows the possibility of inappropriate local ablation of early invasive lesions missed at punch biopsy. The onus of accurate diagnosis lies on the colposcopist. We have studied 1143 patients managed with loop diathermy and identified 35 invasive squamous carcinomas and 9 invasive adenocarcinomas. The data show that the cut-off for accurate colposcopic detection of invasive squamous lesions is not breach of the basement membrane but invasion up to a depth of 1 mm. On the other hand, colposcopy is an unreliable guide for the diagnosis of early adenocarcinoma. Diagnosis based on loop excision allows accurate, rational individualization of management for the unexpected diagnosis of colposcopically occult early invasive disease whilst retaining the logistic benefits of a 'see and treat' policy.