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Objective To determine whether the conventional large loop excision of the transformation zone (CLLETZ) and the 'top-hat' technique (THLLETZ) differ in (a) completeness of excision of the cervical lesion, (b) depth of cervical tissue excised and (c) adequacy of follow up by cytology and colposcopy. Design Retrospective case review.Setting University Teaching Hospital, London.Sample Five hundred and thirteen consecutive patients matched for age, parity, smoking history and referral cytology who had either CLLETZ (286 -5%) or THLLETZ (227 -44%) for cervical intraepithelial neoplasia (CIN). Methods All procedures were performed or supervised by BSCCP-accredited colposcopists. All cytology and histology were reviewed by two specialist cytohistopathologists. Cervical stenosis was defined as difficulty in or inability in obtaining an endocervical brush smear. Main outcome measures Depth of cervical tissue excised, histology of endocervical margins, post-LLETZ cytologic and colposcopic findings. Results The mean depth of excision in the CLLETZ group was 12.1 mm (SD ¼ 4.4 mm) and 20.8 mm (SD ¼ 6.4 mm) in the THLLETZ group. The incidence of involved endocervical margins was 2.8% in the CLLETZ group and 5.2% in the THLLETZ group (P ¼ 0.1). There was CIN in the 'top-hat specimen' of 10 THLLETZ cases (4.4%, CI ¼ 95%). The first post-treatment cervical smear was inadequate in 5 (4.1%) cases in the CLLETZ group and 20 (11.7%) in the THLLETZ group (P ¼ 0.022). Cervical stenosis was found in 21 (7.7%) cases in the CLLETZ group and in 64 (30.9%) cases in the THLLETZ group (P < 0.0001). Eleven (4%) patients in the CLLETZ group had cytological and/or colposcopic evidence of residual CIN compared with 12(5.8%) patients in THLLETZ group (P ¼ 0.4). In the first follow up assessment, 21.7% of the CLLETZ group had incomplete colposcopy compared with 48.7% in the THLLETZ group (P < 0.0001). Conclusions Compared with the CLLETZ, the THLLETZ (1) removed more cervical tissue but did not have a lower incidence of involved endocervical margins, and (2) resulted in significantly higher incidence of inadequate post-treatment colposcopic and cytological follow up. These data indicate that there is no justification to performing a 'top-hat' LLETZ routinely.