The Quality of Well-being (QWB) Scale combines preference-weighted measures of symptoms and functioning to provide a numerical point in-time expression of well-being that ranges from zero (0) for death to 1.0 for asymptomatic optimum functioning. The QWB includes three scales of function: mobility, physical activity, and social activity. Each step of these scales is associated with preference weights. Preference adjustments for symptoms are also included. This paper describes how this general system was used to evaluate outcomes in three different clinical conditions: acquired immune deficiency syndrome (AIDS), cystic fibrosis, and arthritis. In one study, the QWB was administered to 31 patients participating in evaluation of azidothymidine (AZT) treatment for AIDS. The QWB system demonstrated substantial benefits of AZT treatment in comparison to placebo. In a second study, the QWB and a series of pulmonary function measures were administered to 44 patients with cystic fibrosis. The QWB was demonstrated to be significantly correlated with measures of pulmonary function, including FEV1 and maximal midexpiratory flow rate (MMEFR). In addition, there were significant associations between the QWB and measures of exercise tolerance. In the third study, the QWB and an arthritis-specific measure were administered to 83 arthritis patients before and after their treatment. The QWB was at least as capable of detecting clinical change in this population as was the disease-specific measure. For all three conditions, the QWB considered side effects and benefits of treatment in a common unit. Clinical trial data are cited to suggest that the QWB is a valuable outcome measure in arthritis treatment evaluation. We conclude that the QWB has substantial validity as a general health outcome measure and that the system can be used with different populations.