INTRODUCTION: We tested the feasibility of using neuromuscular ultrasound for non-invasive real-time assessment of diaphragmatic structure and function in a canine model of X-linked myotubular myopathy (XLMTM). METHODS: Ultrasound images in 3 dogs [wild-type (WT), n = 1; XLMTM untreated, n = 1; XLMTM post-AAV8-mediated MTM1 gene replacement, n = 1] were analyzed for diaphragm thickness, change in thickness with respiration, muscle echogenicity, and diaphragm excursion amplitude during spontaneous breathing. RESULTS: Quantitative parameters of diaphragm structure were different among the animals. WT diaphragm was thicker and less echogenic than the XLMTM control, whereas the diaphragm measurements of the MTM1-treated XLMTM dog were comparable to those of the WT dog. CONCLUSIONS: This pilot study demonstrates the feasibility of using ultrasound for quantitative assessment of the diaphragm in a canine model. In the future, ultrasonography may replace invasive measures of diaphragm function in canine models and in humans for non-invasive respiratory monitoring and evaluation of neuromuscular disease. Muscle Nerve 50: 607-609, 2014.