The increasing application of mammography, mainly in screening programs for the early detection of breast cancer, and the high technical standard of imaging has resulted in the detection of clinically occult breast tumors. Considering that only diagnosis at an early stage will be able to change the prognosis of breast cancer, this diagnostic challenge appears to be the most exciting field in both breast imaging and breast pathology. Especially the precursor lesions need to be diagnosed and defined precisely to understand their prognostic significance. In imaging, the morphologic appearance of precursor lesions is usually neither typical nor pathognomonic. They have to be assessed histologically using percutaneous interventions. Recent molecular studies have demonstrated various genetic alterations in the ductal epithelium, with the earliest onset in atypical ductal hyperplasia. The recent WHO classification, which is based on molecular data and histopathological features, attempts to define in particular the precursor lesions and low grade intraductal carcinomas. The clinical importance of the various grades has to be assessed. Intimate cooperation between diagnostic radiologist and pathologist is essential.