Patient-reported outcome measurements (PROMs) are often questionnaires which provide and rate the patient's point of view in the measurement of subjective clinical phenomena such as pain or quality of life. In the first of two articles we describe five of the six developmental phases of a patient-reported outcome questionnaire. Adherence to good methodology throughout the process is of utmost importance to ensure reliable and valid results from studies using PROM. Patients from the target population should be involved in the process to obtain content and face validation, i.e. through focus groups.