Clinical mammography is the key tool for breast cancer diagnosis, but little is known about the impact of the organisational set-up on the performance. We evaluated whether organisatorial factors influence the performance of clinical mammography. Clinical mammography data from all clinics in Denmark in the year 2000 were collected and linked to cancer outcome. Use of the National Institute of Radiation Hygiene register for identification of radiology clinics ensured comprehensive nationwide registration. We used the final mammographic assessment at the end of the imaging work-up to determine sensitivity, specificity and accuracy, the latter using a receiver-operating characteristics (ROC) analysis. In 96,534 clinical mammography examinations, sensitivity was 75% and specificity 99%. The presence of at least one high volume-reading radiologist in the clinic increased accuracy (AUC = 0.91 for 2,000 examinations/year, p = 0.017). The examination volume per clinic showed no clear effect on performance, as accuracy was significantly higher in clinics with a medium number of examinations (AUC = 0.93 for 2,000-4,000 examinations/year and 0.90 for >6,000 examinations/year, p = 0.003). Accuracy was significantly lower in regions with high annual utilisation rate of clinical mammography, which means the proportion of examined women in a region (AUC = 0.90 for 3.0-5.0% annual utilisation rate and AUC = 0.93 for 2.0-2.5% annual utilisation rate, and p = 0.001), indicating that clinical mammography worked best in patient populations of purely symptomatic women. Our data indicate that to increase the accuracy of clinical mammography at the community level, the presence of an experienced radiologist should be prioritised ahead of raising the clinic size. (c) 2006 Wiley-Liss, Inc.