The patient clinical outcome assessment is a very important factor in order to guarantee the patient safety. It is the assessment of patient outcome in respect of mental status, symptoms, or impact of ill health on how the patient functions. This assessment aims to improve the quality of health care in general by predicting the performance of any therapeutic option in terms of benefits or harms. Due to the importance of this field, an in-depth review of current issues regarding the assessment of patient clinical outcome should be carried out. Accordingly, this paper go over three main points: 1) the challenges involved in the assessment of patient clinical outcome; 2) a number of the existing methods for patient clinical outcome assessment; and 3) a discussion of the general conceptual limitations and difficulties of patient outcome quantitative assessment. This paper will advance the understanding of the assessment of patient clinical outcome field in regards to its challenges, methods and conceptual limitations.