Ultrasound (US) evaluation of diaphragm thickness and contractility is an effective tool in neurogenic diaphragm dysfunction. There are limited data about the value of this technique in patients with myopathy.We performed a retrospective chart review of cases with electromyography (EMG) -confirmed myopathy and real-time US evaluation of the diaphragm. Diaphragm thickness and thickening ratio (maximal inspiration/expiration) were measured. Demographic, imaging, pathology, and genetic data were reviewed, and the clinical diagnosis was recorded.There were 19 eligible cases, of which 14 (73.7%) had abnormal US findings. Mean diaphragm thickness was 0.12 cm (SD 0.10), and the mean thickening ratio was 1.29 (SD 0.35). In all cases with abnormal US evaluation, the thickening ratio was abnormal. There were no cases with abnormal thickness alone.US examination can detect diaphragm dysfunction in myopathy. It is important to measure both the baseline thickness and thickening ratio to maximize sensitivity. Muscle Nerve 55: 427-429, 2017.