A woman in her fifties complains of meno- and metrorrhagia, and a subsequent biopsy confirms endometrial cancer. Her attending physician suggests a hysterectomy, and other treatments, as needed. The patient may ask; ‘Doctor, is this operation absolutely necessary? What would happen to me if I decided not to have an operation? … How beneficial will this operation be? … Will it stop my bleeding? … What other problems might the operation cause? … Is my disease serious? How probable is it that I will die from it? … How probable is it that I might die on the operating table? … What other treatments can I expect? …’ In many cultures around the world, where the patient's attitude is generally fatalistic, these questions would not be asked and the physician accepting these questions could be perceived as incompetent. The patient might say, ‘Doctor, you are the specialist, you are university-trained, I pay you to decide for me, you must know …’ Elsewhere, an intelligent and curious patient will demand intelligent and competent answers since they expect the best possible estimation of their chances and not a guess or an impression. The patient is interested in prognosis and this chapter is about the objectives, methodology and evaluation of prognosis.