Gastrointestinal illnesses cause physical, emotional and social impact on patients. Patient reported outcome measures (PROMs) are increasingly used in clinical decision-making, clinical research and approval of new therapies. In the last decade, there has been a rapid increase in the number of PROMs in gastroenterology and, therefore, the choice between which of these PROMs to use can be difficult. Not all PROM instruments currently used in research and clinical practice in gastroenterology have gone through a rigorous development methodology. New drugs and therapies will not have access to the market if the PROMs used in their clinical trials are not validated according to the guidelines of the international agencies. Therefore, it is important to know the required properties of PROMs when choosing or evaluating a drug or a clinical intervention. This paper reviews the current literature on how to assess the validity and reliability of PROMs. It summarises the required properties into a practical guide for gastroenterologists to use in assessing an instrument for use in clinical practice or research.