In the study of the roentgenograms of a large number of patients admitted to the Station Hospital, Miami Beach Training Base (Miami Beach, Florida), for abnormalities of the knee, changes in the soft tissues have been noted which have greatly facilitated the diagnosis of effusion into the knee joint. These findings are reported since the usually accepted roentgen signs of knee-joint effusion, i.e., anterior displacement of the patella and widening of the joint (3) have been found entirely inadequate in the x-ray diagnosis of this condition. In a review of the literature, it was found that Lewis (4) mentions the presence of a pyriform mass in the suprapatellar pouch and bulging of the infrapatellar ligament in knee hydrarthroses, but does not describe these abnormalities in detail. Lohr and Hellpap (6) report a fullness in the recess above the upper portion of the knee cap in the presence of intra-articular effusion. Other references to the findings to be described have not been discovered. A brief descrip...