In 2004, all French departments, with the exception of French Guiana, implemented the national organized screening program in accordance with the specifications of the French guidelines published in 2001. Data were analyzed for 97 departments, representing 1,608,397 women screened. The participation rate was 40.2% in 2004. For the 57 departments that had been active for at least 18 months, the estimated participation rate for the two years 2003 and 2004 was 38.6%, and 15 departments had a rate of 50% or higher. In 2004, primary radiologists deemed 10.9% of mammograms abnormal, and 40% of these were still deemed abnormal after follow-up, representing 4.3% of all women screened. This immediate follow-up, which in most cases consists of an ultrasound, cleared 60% of the images (and avoided a subsequent recall). In cases where abnormalities were confirmed, it allowed for immediate treatment. Second-reader radiologists reviewed 95.2% of the images and recalled 1.8% of women for a radiological abnormality, while 0.2% of them had already undergone an immediate follow-up deemed negative on the first reading. A follow-up mammogram was prescribed (for monitoring) for 3.4% of screened women. Cytological and histological examinations (micro- and macro-biopsies) were performed on 0.6% of screened women. Among the 0.8% of women who underwent a surgical biopsy, 73.9% were diagnosed with cancer. The effectiveness and quality indicators are in line with European standards at the national level. The rate of cancers detected through screening is 6.7 per 1,000, of which 6.7% were detected by the second reader alone. The percentage of small cancers with a favorable prognosis is 13.4% for ductal carcinoma in situ, 37% for invasive cancers ≤ 10 mm, and 31% for invasive cancers ≤ 10 mm without lymph node involvement. (R.A.)