BACKGROUND: "Patient-Reported Outcome" (PRO) is used as an umbrella term for different concepts for measuring subjectively perceived health status e. g. as treatment effects. Their common characteristic is, that the appraisal of the health status is reported by the patient himself. In order to describe the informative value of PRO in Health Technology Assessment (HTA) first an overview of concepts, classifications and methods of measurement is given. The overview is complemented by an empirical analysis of clinical trials and HTA-reports on rheumatoid arthritis and breast cancer in order to report on type, frequency and consequences of PRO used in these documents. METHODS: For both issues systematic reviews of the literature have been performed. The search for methodological literature covers the publication period from 1990 to 2009, the search for clinical trials of rheumatoid arthritis and breast cancer covers the period 2005 to 2009. Both searches were performed in the medical databases of the German Institute of Medical Documentation and Information (DIMDI). The search for HTA-reports and methodological papers of HTA-agencies was performed in the CRD-Databases (CRD = Centre for Reviews and Dissemination) and by handsearching the websites of INAHTA member agencies (INAHTA = International Network of Agencies for Health Technology Assessment). For all issues specific inclusion and exclusion criteria were defined. The methodological quality of randomized controlled trials (RCT) was assessed by a modified version of the Cochrane Risk of Bias Tool. For the methodological part information extraction from the literature is structured by the report's chapters, for the empirical part data extraction sheets were constructed. All information is summarized in a qualitative manner. RESULTS: Concerning the methodological issues the literature search retrieved 158 documents (87 documents related to definition or classification, 125 documents related to operationalisation of PRO). For the empirical analyses 225 RCT (rheumatoid arthritis: 77; breast cancer: 148) and 40 HTA-reports and method papers were found. The analysis of the methodological literature confirms the role of PRO as an umbrella term for a variety of different concepts. The newest classification system facilitates the description of PRO measures by construct, target population and the method of measurement. Steps of operationalisation involve defining a conceptual framework, instrument development, exploration of measurement properties or, possibly, the modification of existing instruments. Seven out of 59 RCT analysing the effects of antibody therapy for rheumatoid arthritis define PRO as the primary endpoint, 38 trials utilize composite measures (ACR, DAS) and ten trials report clinical or radiological parameters as the primary endpoint. Six out of 123 chemotherapy trials for breast cancer define PRO as the primary endpoint, while 98 trials report clinical endpoints (survival, tumour response, progression) in their primary analyses. Discrepancies in the number of trials result from inaccurate specifications of endpoints in the publications. This distribution is reflected in the HTA-reports: while almost all reports on rheumatoid arthritis refer to PRO, this is only the case in about half of the reports on breast cancer. CONCLUSIONS: As definition and classification of PRO are concerned, coherent concepts are found in the literature. Their operationalisation and implementation must be guided by scientific principles. The type and frequency of PRO used in clinical trials largely depend on the disease analysed. The HTA-community seems to pursue the utilization of PRO proactively - in case of missing data the need for further research is stated.