The patient's opinion is central to the monitoring and improvement of health outcomes. The goal of treatment should be the preservation of function and well-being of the patient. Despite this, standardized assessments of patients' experiences of disease and treatment are not routinely collected in clinical research and medical practice. In an era of cost containment, it is essential to monitor health outcomes. A prototype for collection of relevant data can be found in the Medical Outcomes Study which tests methods for monitoring the results of medical care among patients with hypertension and other conditions. Results from this study have shown that there is good reason to be optimistic about the feasibility of standardized, self-administered questionnaires as a primary means of collection for patient outcome data. Furthermore, it is possible to create an enhanced data base and add to it routinely on a large scale across diverse health care settings. Details of the health outcome measures used in the Medical Outcomes Study are presented in this paper.