OBJECTIVES: Cost of illness analysis of breast cancer in Austria using mainly Austrian billing data from intramural and extramural medical treatment based on data from 2006/07 for treatment and degree of severity evaluation. Regarding this project a detailed treatment course classification has to be realized to evaluate the costs and patient ways in Austrian health system. METHODS: Main strategy of the project is the combination of data samples detected by Austrian cancer registry and billing data of intramural and extramural single person datasets in combination with intake data of medication for each patient. By combining the recorded data from national statistics, including TNM-classification of each new breast cancer case, and the ICD10-diagnoses, as well as medical individual services, results in classification of breast carcinoma on single person level are achieved. For separation of drug treatment concerning chronical diseases versus cancer indicated drug administration, the half year time span before the first mamma carcinoma detection and the year afterwards is analyzed separately. Special medication groups are assessed in detail and inclusion/exclusion – criteria for costs and treatment are defined. RESULTS: Based on this identification an alternative subsumption of new detected carcinoma in six groups (hormone receptor positive, Her 2 positive, hormone receptor positive and Her 2 positive, triple negative, metastasizing mamma carcinoma, early stage mamma carcinoma without chemo therapy in course of treatment) is defined. CONCLUSIONS: This classification leads to better insights for cost evaluation representing the state of the art in Austria. This strategy also leads to better overall reliability because the margin of uncertainty of the parameters can be reduced significantly.