OBJECTIVES: To describe the views of the British public on the use of personal medical data by the National Cancer Registry without individual consent, and to assess the relative importance attached by the public to personal privacy in relation to public health uses of identifiable health data. DESIGN: Cross sectional, face to face interview survey. SETTING: England, Wales, and Scotland. PARTICIPANTS: 2872 respondents, 97% of those who took part in the Office for National Statistics' omnibus survey, a national multistage probability sample, in March and April 2005 (response rates 62% and 69%, respectively). RESULTS: 72% (95% confidence interval 70% to 74%) of all respondents did not consider any of the following to be an invasion of their privacy by the National Cancer Registry: inclusion of postcode, inclusion of name and address, and the receipt of a letter inviting them to a research study on the basis of inclusion in the registry. Only 2% (2% to 3%) of the sample considered all of these to amount to an invasion of privacy. Logistic regression analysis showed that the proportions not concerned about invasion of privacy varied significantly by country, ethnicity, socioeconomic status, and housing tenure, although in all subgroups examined most respondents had no concerns. 81% (79% to 83%) of all respondents said that they would support a law making cancer registration statutory. CONCLUSIONS: Most of the British public considers the confidential use of personal, identifiable patient information by the National Cancer Registry for the purposes of public health research and surveillance not to be an invasion of privacy.