Roentgencephalometric tracings of skulls of 7-week-old normal and muscular dystrophic mice were compared. A marked size reduction of the dystrophic skulls relative to the normal ones was observed. However, the visceral parts of the dystrophic skull were more reduced in size than the neural parts. Marked differences in shape were also noticed. Differences in angular values were primarily found between skull parts, whereas angles between adjacent bones were remarkably similar in the two groups. Only a few exceptions of this condition were observed, as angles between adjacent bones in the posterior part of the cranial vault of the dystrophic animals differed from those of the normal animals. The observed differences between normal and dystrophic mice skulls may chiefly be explained as the results of differences in the action of diseased and normal muscles on bone.