We compared the magnetic resonance images of the tongues of 16 amyotrophic lateral sclerosis (ALS) patients with those of 20 control patients and found the tongue in ALS patients is more frequently and more severely involved than suspected clinically, with major abnormalities of size, shape, position, and internal structure. The tongue size in ALS, as measured in the sagittal plane, can be reduced by as much as two-thirds of normal. The shape of the tongue in ALS tends to be rectangular or square rather than curved as is normal. As severity of the disease increases, the position of the tongue changes so that the bulk of the muscle falls away from the incisors and no longer is in contact with the hard or soft palate. The normal radial bands from the anterior floor of the mouth to the mucosal surface are often missing in ALS as are the two curvilinear bands that run parallel to the mucosal surface and intersect the radial bands. Also, there is a mottled disorganization of the internal structure of the tongue with areas of increased and decreased signal intensity.