This article illustrates and provides an update on lesions considered to be precursors of mammary carcinoma or indicators of elevated risk for subsequent development of carcinoma.A review of usual ductal hyperplasia and ductal carcinoma in situ is given to provide a background reference for comparison with the high-risk lesions. Lesions illustrated and described as high-risk include atypical ductal hyperplasia, atypical columnar cell hyperplasia, lobular carcinoma in situ, atypical lobular hyperplasia, and proliferative radial scar lesions.