The objectives of our study were to analyse the use of diagnostic mammography among nonattenders and attenders in organised mammography screening in Denmark in 2000, to assess the contamination from organised screening of noninvited age groups and to measure the impact of local policy on opportunistic screening. Data on all diagnostic mammographies performed in Denmark in 2000 and data on women targeted by the 2 organised mammography screening programmes in Copenhagen and the county of Fyn were collected. All data were linked by the Danish personal identification number. Information on the official policy in 2000 with regard to opportunistic screening was collected from all counties. The proportion of women using diagnostic mammography was only 1-3% for both attenders and nonattenders in organised mammography screening, but it was significantly higher in Copenhagen than in Fyn, due to availability of mammography in private clinics. The proportion of women using diagnostic mammography varied from 1-4% across counties. The official policy on access to diagnostic mammography and contamination from organised mammography screening of adjacent age groups had no impact on the use. Instead, urbanisation was positively correlated with use of diagnostic mammography. In conclusion, our results clearly showed that nonattenders in organised mammography screening programmes do not seek mammography outside the programme. Since a positive policy toward opportunistic screening did not have any effect, our results add further evidence to existing knowledge that the only reasonable way to achieve high mammography coverage is through a well-organised screening programme.