The concept of "patient-reported outcomes" have been proposed by the Food and Drug Administration in the year 2000, in order to describe one of the different and potential sources of information on the drug's safety and effectiveness. It represents an "umbrella" term, which covers a multiplicity of meanings and primarily identifies a conceptual approach and a methodology specifically oriented to the patients' point of view on outcomes, instead of the traditional clinical and professional perspective. The patient-reported outcomes measures are frequently self-completed questionnaires. The measures can be classified in general and specific. The first one, general, relates to the assessment of the quality of life or the health status, in the general population or in subgroups with particular health problems (eg. SF-36 Health Survey, EQ-5D). The second one, specific, mainly relates to the assessment of particular types of symptoms (eg. pain, anxiety, fear, depression) and functions (eg. daily living activities), in population's subgroups with definite health problems, undergoing or not to a healthcare procedure (eg. Adult Asthma Quality of Life Questionnaire, Kidney Disease Quality of Life Instrument, Oxford Hip Score, Oxford Knee Score). For the selection of an instrument a series of criteria needs to be taken into account, among which the psychometric properties, the expert judgement, the interpretability, the acceptability, and the feasibility of the entire process.