This presentation describes the organization and first-round results of the Stockholm mass mammography screening program, and discusses ways of checking the quality of an ongoing screening program. The Stockholm mammography screening program started in 1989 at five independent screening units, and comprises more than 150,000 women aged 50 to 69 years. The first round was completed in June 1991. Compliance during the studied period was 70.6%, and the recall rate was 3.0% of the attending women. Breast cancer was diagnosed in 676 women, of whom 90 (13.3%) had a cancer in situ. The cancer prevalence rate was thus 6.3 cancers per 1,000 screened women. Surgery was performed on 925 women, of whom 249 had benign lesions, giving a benign/malignant ratio of 0.37 to 1. Fifty-two per cent of the cancer patients were operated with breast conserving surgery. The median size of the invasive cancers was 12 mm; almost 80% were node-negative. Experience from the first two years of this mass mammography screening program shows that it meets the major quality requirements. One of the main future goals is to maintain the high quality of the program. Another important goal is a further increase in compliance.