Quality of life (QOL) questionnaires are integrated into clinical trials in order to evaluate different treatments, and rarely used in a diagnostic sense. The aim of this study was to identify clinically meaningful subgroups by means of established QOL tools. Since January 1995, a field study funded by the German Ministry of Health was conducted to evaluate quality of care of breast cancer patients in eastern Thuringia. During the follow-up period, the European Organization of Research and Treatment of Cancer (EORTC), Quality of Life C30 and the breast specific module BR23 were mailed. One-hundred-fifty-eight women answered both questionnaires. A cluster analysis was performed to distinguish subgroups on the basis of QOL-BR23 scores. According to the QOL outcomes, four subgroups could be described. There was a strong relation to operative treatment (p < 0.05), while no association with the adjuvant treatment strategy was observed. The subsets identified on the basis of BR23 scores were significantly related to all C30 domains. It was possible to demonstrate the clinical validity in terms of clinical and sociodemographic data. No association was found with the marital status or the highest level of education, while a worsening of the financial situation was associated. It could be shown that a distinction of patient subgroups based on clinically meaningful BR23 data is possible. Subgroups with specific profiles could be identified. In the future, the characterisation of subgroups could provide a possibility to generate indications for specific supportive interventions.