The frequency of certain medical procedures and their results vary strongly between countries, and also between regions within one country. These variations in clinical practice mean the quality of healthcare is suboptimal, result in unnecessary expense and patients are at risk of complications caused by unnecessary interventions. Patient Reported Outcome Measures (PROMs) are an instrument to clarify if a patient has benefited from a certain treatment. Systematic measurement of PROMs is necessary to show relevant differences in the effect of a therapy. If data of differences in results are combined with those of regional variations in clinical practice, it will become clear where too much or too less is treated. We expect that the systematic measurement of PROMs will make a valuable contribution to improving the quality of Dutch healthcare.