Introduction This review presents an analysis of 90 consecutive surgically treated popliteal cysts in 84 (private and service) patients at The Hospital for Special Surgery from 1938 to 1960. In particular it contrasts the clinical differences in the adult and children's popliteal cyst. A strikingly high incidence of popliteal cysts, occurring at the midportion of the first decade in children, is noted in this series. The curious absence of associated joint disease and a salient history in children, as contrasted with the presence of such findings in adults, suggests a dissimilar etiology for the two age groups. The precise similarity, however, of the anatomical origin of the cyst in each group suggests common factors. The earliest mention of popliteal cysts in the literature was by Adams in 1840. He described an enlargement of the bursa beneath the medial head of the gastrocnemius which communicated with the knee joint, and which