Introduction: When preparing for clinical trials in myotonic dystrophy type‐1 (DM1), it is important that researchers develop and identify patient‐reported outcome measures with good measurement properties. Methods: Fifty‐two DM1 patients enrolled in 2 clinical studies completed the Myotonic Dystrophy Health Index (MDHI), 36‐Item Short Form Health Survey (version 2; SF‐36v2), Individualized Neuromuscular Quality of Life questionnaire (INQoL), and a questionnaire comparing the relevance, usability, overall preference, and perceived responsiveness of each measure. The associations between instrument scores and physical function, genetic test results, and employment status were examined. Results: The MDHI was preferred over the INQoL in 13 of 13 areas and was preferred over the SF‐36v2 in 9 of 13 areas. The MDHI was the only score that was associated with participant employment status, CTG repeat length, and the 3 measurements of clinical function. Discussion: The MDHI correlates well with physical function and is viewed favorably by participants in DM1 clinical studies. Muscle Nerve 58: 49–55, 2018