Objectives: To evaluate the early outcome of an organised mammography screening programme in an area with little opportunistic screening. Setting: The municipality of Copenhagen, Denmark, during four invitation rounds 1991-99. Methods: The following outcome measures were used: rates of participation, recall, false positive, and cancer detection. Benign biopsy, distribution of tumour size, lymph node status, and malignancy grade. Results: A total of 106 933 screens were undertaken, and 824 invasive breast carcinomas or CIS were detected. The detection rate was 11.9 per 1000 participants in the first invitation round, and it continued to be high in subsequent rounds. The percentage of CIS cases was 11%. Coverage declined from 71% in the first round to 62% in the fourth, although 91% of those participating in the previous three rounds attended. The programme operated with a high recall rate. The false positive rate was also high, being 5.6% at first screen, and 1.8% later on. However, 90% of false positives were sorted out already at assessment. The percentage of screen detected invasive breast cancers with a tumour diameter ≤10 mm was 39% compared with 16% of all invasive breast cancers in these age groups in Copenhagen before screening. Conclusion: Copenhagen is an area with a high incidence of breast cancer and with relatively little opportunistic screening. The start of a screening programme with a high recall rate in this area resulted in a detection rate above 1%. The Copenhagen programme met or exceeded most of the interim measures recommended in the European Guidelines.