In recent years, the importance of patient-reported outcomes(PRO)in addition to clinician-outcome assessment has been particularly recognized in clinical trials and routine clinical care of practice. PRO is defined as "any report of the status of a patient's health condition that comes directly from the patient, without interpretation of the patient's response by a clinician or anyone else". For example, in oncology field, NCI-CTCAE has conventionally been used for adverse event assessment. However, it has been pointed out that the adverse event reported by medical staffs tends to underestimate as compared by patients themselves. Hence, PRO version of the Common Terminology Criteria for Adverse Events(PRO-CTCAE), is expected to play an important role. In this article, the background of importance of PRO in oncology, the role of PRO in clinical outcome assessments, the difference between PRO and QOL, significance that PRO evaluation brings to patients and clinical practice, PRO-CTCAE and recent methodology of PRO research will be overviewed.