THE RECENT radiological literature has contained little information concerning spontaneous Achilles' tendon rupture. Although the clinical and physical findings were thoroughly described by Petit (1) in 1726, only one reference to this entity could be located in the current radiological literature (2). A review of this subject was undertaken in the light of what is felt by the authors to be specific and highly diagnostic roentgenographic findings. Most Achilles' tendon ruptures are of the spontaneous type, with no direct tendon trauma and no break in the skin. The rupture occurs as a separation of the tendon in its body or insertion, or in the musculo-tendinous portion. The history, symptoms, and clinical findings will usually be quite specific. If these are not clear-cut, the roentgenographic signs may be diagnostic and prevent undue delay of surgical treatment. The roentgenographic findings are: (a) obscuration of the tendon; (b) posterior encroachment on the fat pad ; (c) soft-tissue mass at the tendon...