OBJECTIVES: Patient-reported outcomes (PRO's) are an increasingly popular endpoint in clinical trials and outcomes studies. However, PRO's do not occur in isolation; they are filtered through personality and attitudes. This study defines attitudinal segments among European Health care consumers and identifies the clinical implications. METHODS: Analyses are based on 17,341 responses to questionnaires mailed to adults in France, Germany, and Great Britain in 2002. Results are weighted and projected to the national populations of each country, based on gender, age, and region. Respondents indicated how strongly they agreed with 18 attitudinal statements, categorized as: in control of health; faith in physicians; fatalistism; compliance; experimentation; and information seeking. A k-means cluster analysis was performed, with mean substitution for missing values. The solution was validated using split samples. Clusters were compared by demographics, health habits, quality of life (SF-8), and resource use. RESULTS: The analysis yielded a five cluster solution. "Traditional" (16%) have faith in physicians and are not experimental. "Open-Minded" (25%) are willing to explore both traditional and alternative Health care options. "Independent Thinkers" (19%) make their own Health care decisions. They feel in control of their health and are experimental. "Health care Roulette" (22%) are gambling with their health. They are fatalistic, but still experimental. "Apathetic" (19%) are not engaged in their Health care. Clusters differed by outcomes. "Traditional" and "Independent Thinkers" experience high physical and mental well-being. "Open-Minded" are generally in poor physical health with a high rate of multiple comorbidities. Consistent with their fatalistic attitudes, "Health care Roulette" and "Apathetic" have the worst health habits and experience low physical well-being. CONCLUSIONS: PRO's should be interpreted within the context of the reporting patient's attitudes. Understanding and measuring attitudinal complexity should be considered in designing and interpreting studies of resource use, adherence, and quality of life and in developing programs for delivery of care.