summary Popliteal Cysts are common soft tissue masses in children that unlike the adult population, are most often not associated with meniscal tears. Diagnosis is suspected clinically with a palpable mass in the popliteal fossa that transilluminates. MRI can confirm the diagnosis of a cystic lesion. Treatment is observation as the majority of lesions spontaneously resolve. Etiology Pathoanatomy popliteal cysts usually are located between muscles of semimembranosus medial head of gastrocnemius from herniated posterior knee joint capsule synovium Anatomy Muscles posterior to medial knee capsule semimembranosus medial head of gastrocnemius Presentation Symptoms usually asymptomatic Physical exam located in popliteal fossa usually located medially and distal to knee crease most pronounced with knee extended mass will transilluminate Imaging Radiographs are normal Ultrasound consistent with cystic lesion MRI show fluid filled cyst Treatment Nonoperative observation indications mainstay of treatment with majority of cases resolving spontaneously Operative excision indications only if cyst causes significant discomfort failure of spontaneous resolution