The study of outcomes has become essential for guiding quality-of-care assessment and for clinical research. In this article, the properties and process of patient outcomes measurement are described. The limitations of traditional outcomes are discussed and contrasted with the emerging concept of "patient-centered" outcomes, measured by validated instruments to assess the effects of surgical interventions on health-related quality of life, functional status, pain, and patient satisfaction. The strengths and weaknesses of several measurement tools used in the surgical literature are evaluated. Finally, the authors introduce "composite outcomes" as a reflection of the multidimensional nature of modern patient care.