In the past 2 decades, outcome assessment following knee surgery has focused increasingly on the patient's perspective. While traditional measures of outcome, including physical examination, imaging studies, and measures of knee laxity are complementary, questionnaires have become more important in determining the value of a procedure. Reliability, validity, and responsiveness are all important measurement qualities for health-related quality of life instruments. There are several questionnaires available, both for active patients with disorders of the knee, as well as for older patients with degenerative conditions. Activity level is also an important prognostic variable for patients with disorders of the knee. Clinical researchers should also use a validated activity rating scale to evaluate what patients are doing, in addition to how they are doing.