Prognostic studies assess outcomes of a disease and how likely they are to occur over time. For surgeons, this informs treatment recommendations and answers patients’ questions about possible outcomes after surgery. Therefore, knowing how to search for and evaluate prognostic studies is fundamental. Prognosis can be studied through a variety of designs where the optimal design depends on the question. Generally, observational studies provide the highest quality information when estimating prognosis. Evaluating a prognostic study hinges on six sequential questions: (1) Is the sample representative of my patient?, (2) Is the follow-up sufficiently long and complete?, (3) Are the assessed outcomes objective and unbiased?, (4) How likely are the outcomes to occur over time?, (5) How precise are the estimates?, and (6) Can I apply the results to my practice or patient? This chapter demonstrates how to identify and appraise prognostic studies by answering each question for a clinical example.