This paper describes compliance with the completion of a quality of life questionnaire in the Breast Cancer Prevention Trial, a large multi-centre randomized trial that is studying the efficacy of Tamoxifen in preventing breast cancer. In the first 4875 women enrolled in the control arm of the study, there was a very high rate of questionnaire completion at baseline, 3 months, 6 months and 12 months of follow-up (89.8 per cent completed forms at 12 months). The sample was examined according to demographic and risk factors, as well as by recruitment cohort. There was a significantly poorer compliance rate for the most recently recruited cohort that was followed-up during a time of substantial external negative publicity related to clinical trial research. Nevertheless, the overall compliance with completion of quality of life data in this trial is very high, which is probably attributable to the high educational status of the trial participants.