Measuring patient-reported outcomes is the current method for conducting clinical research. Creating a new outcome measure is an exhaustive process that should be carefully monitored and concentrated on only important and common conditions. The evaluation of an existing outcome measure should involve assessing its internal consistency, reliability, floor and ceiling effects, validity, and ability to measure clinically meaningful change. The most important characteristic of a patient-reported outcome is that it is developed with direct input from its target patient population. Item generation and reduction is the most critical step in the development process because it "guarantees" that patients have communicated what is important to them and represents content validity. Outcome measures should not change; rather, they should demonstrate responsiveness by being reproducible and reliable if a patient's clinical condition is stable or reflect differences if a patient's clinical condition varies. Validation is an iterative process and requires patients from different settings and circumstances.