Background Spinal Muscular Atrophy (SMA) is manifested by deformation of the chest wall, including a bell-shaped chest. We determined the ability of a novel non-ionizing, non-volitional method to measure and quantify bell-shaped chests in SMA. Methods A 3D depth camera and a chest X-ray (CXR) were used to capture chest images in 14 SMA patients and 28 controls. Euclidean and geodesic chest and abdominal distances were measured from the 3D images, and horizontal distances were measured from the CXR images. The ratio of the chest to abdominal distances was used to quantify chest shape in both the 3D depth camera and the CXR, and both were compared between healthy and SMA patients. Results The mean 3D Euclidian ratio of distances was 1.00 in the control group and 0.92 in the SMA group ( p = 0.01), the latter indicative of a bell-shaped chest. This result repeated itself in the geodesic measurements (0.99 vs. 0.89, respectively, p = 0.03). Conclusion The herein-described novel noninvasive 3D method for measuring the chest and abdominal distances was shown to distinguish the bell-shaped chest configuration in patients with SMA from the normal chests of controls. This method bears several advantages over CXR and may be readily applicable in clinical settings that manage children with SMA.