['To determine, within the UK, the stage and grade of prostate cancers that would be found through population-based prostate specific antigen (PSA) testing and biopsy.', "In the 'Prostate Testing for Cancer and Treatment' trial (ProtecT), men aged 50-69 years were recruited from nine cities in the UK and from randomly selected practices of general practitioners. Those with a PSA level of >3 ng/mL were offered a prostate biopsy. Age, PSA, stage and grade at diagnosis of ProtecT participants with cancer were compared with contemporaneous incident cases aged 50-69 years (age-restricted Cancer Registry cases) registered with the Eastern Cancer Registration and Information Centre (ECRIC).", 'Within ProtecT, 94,427 men agreed to be tested (50% of men contacted), 8807 ( approximately 9%) had a raised PSA level and 2022 (23%) had prostate cancer; 229 ( approximately 12%) had locally advanced (T3 or T4) or metastatic cancers, the rest having clinically localized (T1c or T2) disease. Within ECRIC, 12,661 cancers were recorded over the same period; 3714 were men aged 50-69 years at diagnosis. Men in ProtecT had a lower age distribution and PSA level, and the cancers were of lower stage and grade (P < 0.001 for all comparisons). If population-based PSA testing were introduced in the UK, approximately 2660 men per 100,000 aged 50-69 years would be found to have prostate cancer, compared to current rates of approximately 130 per 100,000. If half of men accepted PSA testing, approximately 160,000 cancers would be found, compared to 30,000 diagnosed each year at present.'] Does population-based prostate-specific antigen testing in the UK lead to a stage migration of prostate cancer?