Publisher Summary Health related quality of life is a subjective parameter commonly used to assess the views of the patients in terms of the physical, social, and emotional aspects of living with their condition. Direct questioning is a simple and appropriate way of accruing information about how patients feel and function. Using standardized questionnaires ensures well-documented psychometric properties. For routine application in clinical practice or in clinical trials, it is essential that the instruments employed are simple and comparatively short. The majority of patients or probands welcome the opportunity to report how symptoms and their subsequent treatment affect daily life. Psychometrically evaluated questionnaires allow uniform administration and unbiased quantification of data because the response options are predetermined and thus equal for all respondents. Certain difficulties introduce bias into the interpretation of data. These include the experiences of some interviewed old age individuals, particularly of older ages who might have difficulty with reading or writing, or who have been exposed to less experienced interviewers, or simply the expenses involved in gathering quality-of-life data. Standardization, compatibility, eradication of possible bias, and economy are therefore important variables for the validity of any type of quality-of-life assessment. The application of health related quality-of-life instruments requires the same scrutiny and intention as the measurement of physiologic outcomes.