Recent efforts at reducing health care expenditures and practice variations have focused attention on treatment appropriateness, patient preference, and quality of life as important elements of treatment evaluation. These characteristics of medical treatment can be assessed by administration of a structured, valid health status assessment questionnaire before and at fixed intervals following treatment, and standardized scores may be compared to normal scores derived from healthy, untreated populations. One hundred valve replacement patients completed a standardized questionnaire, the 'SF-36', preoperatively and at 1- and 6-months postoperatively. Preoperatively, valve replacement patients are substantially impaired in their physical capacity, their ability to function in important roles, and their vitality. At one month, they report significant decrements in social and role functioning and in pain which we attribute to the trauma of surgery and recovery. At six months, mean scores approximate those for sex- and age-matched normals except for persistent moderate impairment in role functioning. Post-operative functional impairment is greatest for those undergoing mitral valve replacement, particularly when coronary artery grafts are performed concurrently, and for patients receiving bioprosthetic valves. Structured health status assessment provides a useful adjunct to other methods of assessing clinical status and evaluating treatment outcomes.