Accepted wisdom holds that high compliance is essential for a screening programme to be successful.Indeed, a reason that the national breast screening programme is not routinely offered to women aged 65 or more is on the grounds of predicted poor compliance by older women. Increasing compliance is often associated with increased costs. These costs represent a lost opportunity for screening alternative target populations. We question the need for screening programmes to achieve high compliance, and we argue that a screening programme can be efficient with very low levels of compliance. Adopting compliance as a screening objective and as a measure of the success of screening may be detrimental to the efficiency of a screening programme.