Objective The objective of this study was to compare the sensitivity of cervical cytology using conventional smears and SurePath liquid-based cytology (LBC).Design Prospective randomised evaluation of diagnostic test.Setting A single institution colposcopy clinic.Population Women attending first visit colposcopy appointments were offered entry into the study.Methods Cervical cytology samples from 913 women of age 16-75 years were randomly processed as SurePath LBC or conventional smears. Conventional smears were taken for 453 women and a SurePath LBC taken for 451 women. Cytology results were correlated with colposcopic findings and histology from colposcopic biopsies, treatment and follow up.Main outcome measures To compare the sensitivity of SurePath LBC and conventional smears for histologically proven abnormality.Other outcome measures include a comparison of their sensitivity for high-grade abnormalities and their satisfactory rate.Results Accounting for all randomised samples, there was a trend towards improved sensitivity for SurePath LBC (79.1 versus 73.7%, P = 0.1). However, excluding unsatisfactory cytology (and samples not taken) eliminated this trend; the sensitivity for both LBC and conventional smears for any epithelial abnormality was 81%. With a threshold of atypical squamous cells of uncertain significance (ASC-US), both SurePath LBC and conventional smears had a sensitivity of 92% for high-grade lesions. SurePath LBC was less likely to be reported as unsatisfactory (2.7 versus 9.1%, P < 0.0001).Conclusions In this context, with a threshold of ASC-US, both SurePath LBC and conventional smears offer high sensitivity for the detection of CIN2/3, but SurePath LBC is less likely to be reported as unsatisfactory.Keywords Cervical cytology, liquid-based cytology, sensitivity, SurePath.Please cite this paper as: Sykes P, Harker D, Miller A, Whitehead M, Neal H, Wells J, Peddie D. A randomised comparison of SurePath liquid-based cytology and conventional smear cytology in a colposcopy clinic setting.