In addition to nationwide standardized pathology forms for operable primary invasive breast cancer, the Danish Breast Cancer cooperative Group (DBCG) in 1982 introduced pathology forms for breast cancer in situ (CIS). The histological reporting form was used primarily for ductal cancer in situ (DCIS) treated with wide local excision. The form however, also provided information on lobular carcinoma in situ (LCIS), atypia and benign lesions. In 1989 the reporting form for DCIS was extended and now provided information on histological subtype, malignancy grade, growth pattern and both Estrogen receptor (ER) and Progesteron receptor (PR) status. Also mastectomy specimens were included. In 2004 the previous malignancy grading was replaced by the Van Nuys classification, and information on microcalcifications was introduced. The axillary status now included the sentinel node technique only. In 2006 the pleomorphic subtype of LCIS was added to histological subtypes. The present work reviews the DBCG guidelines and recommendations concerning CIS adding a brief characterization of the Danish CIS population. It also refers to the introduction of modern molecular pathology and distinction between low-risk and high-risk CIS lesions. A major point is that without the thirty years of outstanding efforts by the DBCG, future research would not be able to meet expectations.