Introduction. Since 30 years, DBCG (Danish Breast Cancer Cooperative Group) has maintained a clinical database allowing the conduct of quality control studies, of randomised trials, examination of the epidemiology of breast cancer and of prognostic and predictive factors. Material and methods. The original database included patients with invasive breast cancer, but has later been expanded to patients with in situ breast cancer and hereditary breast and ovarian cancer families. Results. The multidisciplinary cooperative group has provided successive treatment guidelines and 70% of the 77284 registered patients have been enrolled and received treatment according to these guidelines. The standard treatments and the randomised trials included in the DBCG programmes are all briefly described. Among high-risk patients 48% have participated in randomised trials, and the results of these trials have largely been implemented in the next generation of treatment guidelines. Records within the clinical database of archival tumour tissue have established a basis for translational research and epidemiologic research has been enabled through linkage to other healthcare registries. Discussion. The joint conception of the multidisciplinary breast cancer group and a clinical database has provided improvements in the management of breast cancer patients and has enabled recruitment of patients onto randomised trials.