The five-year screening experience for 10,128 asymptomatic women whose conditions were evaluated at the Louisville Breast Cancer Detection Demonstration Project disclosed 163 breast carcinomas in women aged 35 to 74 years. Thirty-four percent of patients with proved carcinoma were younger than 50 years; 31% with infiltrating carcinoma had axillary metastases at the time of diagnosis. In younger patients, carcinomas disclosed at intervals between scheduled screenings were more commonly metastatic. Minimal breast cancer was more prevalent in the screened population (29%) than the unscreened population (less than 5%), and appeared with similar frequency in screenees of each age category. Screening women younger than 50 years allows earlier diagnosis and treatment of breast cancer in a favorable stage that is comparable with that noted in the older screenees.