Functional popliteal artery entrapment syndrome (FPAES) is an uncommon overuse injury in young physically active adults manifest by neuromuscular symptoms (gastroc/soleus cramping, plantar paresthesias). It is commonly confused with chronic recurrent exertional compartment syndrome (CRECS). This study evaluated the diagnostic testing, mechanism of injury, and treatment differences between FPAES and CRECS.Between 1987 and 2007, 854 patients (557 women, 297 men; mean age, 28.5 years) were surgically treated for the diagnosis of CRECS or FPAES, or both. Compartment pressures were measured in all patients who had anterior lateral or posterior superficial calf symptoms (normal pressure or=25 mm Hg), and fasciectomy was performed for CRECS under local anesthesia (anterior lateral, 508; posterior superficial, 191; distal deep posterior, 101). The result of stress plethysmography was positive in 139 (18%), but they were asymptomatic. Forty-three patients (27 women, 16 men; mean age, 26.6 years) had positive stress plethysmography, appropriate FPAES symptoms, and normal compartment pressures. MRA/MRI in all 43 demonstrated normal musculotendinous anatomy and lateral neurovascular compression with plantar flexion. Under general anesthesia, all had excision of the soleal band, with relief from symptoms. In 19 of the 43 FPAES patients (44%), CRECS releases were done before or after FPAES surgery. Follow-up ranged from 12 to 240 months.FPAES and CRECS occur in the same population with similar symptoms but require different treatment.