This study reports on the 20-year follow-up of the women diagnosed with breast cancer in the Breast Cancer Detection Demonstration Project (BCDDP) between 1973 and 1980. This project provided 5 years of screening with physical examination and two-view mammography for 280,000 volunteer women across the United States. Based on a 96% follow-up from 1993 to 1995 of the 4,051 women with breast cancer available for analysis, 2,658 (66%) were alive and 1,393 (34%) were dead. A high proportion of the cancers were detected by mammography alone, and 28.6% of all the cancers were smaller than 1.0 cm. Survival rates were calculated by life table method with deaths from breast cancer as the outcome. The adjusted survival rate for the entire group was 80.5%, and the observed survival rate was 61.7%. Adjusted and observed survival rates were 97.2% and 78.5%, respectively, for women with non-invasive cancers and 78.2% and 59.3%, respectively, for those with invasive cancers. Lymph node status and the size of the cancer at diagnosis were prognostic indicators of survival in the BCDDP Women with invasive cancers and negative lymph nodes had an 85.5% breast cancer survival rate and a 65.6% observed survival rate. Adjusted survival rates for women with invasive breast cancers were 90.2% for cancers smaller than 1 cm, 80.5%, for cancers 1.0 to 1.9 cm, 70.5% for cancers 2.0 to 4.9 cm, and 60.6% for cancers larger than 5 cm. Women 40 to 49 years of age demonstrated a greater survival with noninvasive or invasive cancers smaller than 5.0 cm compared with women 50 to 59 and 60 to 69 years of age at diagnosis. These results from the BCDDP are discussed in the context of the recent decline in breast cancer incidence and mortality in the United States.