Abstract In DMD patients, respiratory muscle weakness induces a severe respiratory failure in the course of the disease. Hence, treating also the dystrophic respiratory muscles is of paramount importance and one of the arguments in favor of systemic therapy. In parallel, there is a need for novel non-invasive outcome measures for the diaphragm muscle, complementary to the histologic evaluation and the radiographic studies previously reported. NMR imaging has proven very efficient to discriminate dystrophic muscles from healthy control ones and even more, successfully treated dystrophic muscles from untreated ones in a loco-regional therapeutic trial of GRMD dogs, the canine counterpart of DMD patients. We investigated the ability of NMR to evaluate the diaphragm, which was imaged with a 3D SPACE T1-weighted sequence in 5 healthy and 8 GRMD dogs (mean age: 13.6 and 14.6 months, respectively), using a 3-tesla NMR scanner. In addition, breath-hold T2-weighted HASTE sequences were performed in 3 healthy and 7 GRMD dogs. In all dogs, diaphragms were visualized, particularly the ventral segment, cranial to the liver. In healthy dogs, it appeared as a thin, homogeneous, T1- and T2-hypointense structure compared to the liver. In GRMD dogs, as early as at 3 months of age, the diaphragm was thickened (11.2 ± 6.0 mm vs 2.4 ± 0.7 mm in healthy dogs), when measured in the sagittal plan, cranially to the liver close to its insertion to the manubrium; p < 0.008). Diaphragmatic signal was hypo-intense on T1w images, hyper-intense on T2w images and heterogeneous on all images of GRMDs.