The authors describe the case of a 32-year-old man with intermittent claudications. Large abnormal muscular structures were found in the popliteal regions, incl. a secondary pterygium on the right. On both limbs these muscles arrested by their pressure during contraction the blood flow in the popliteal artery and caused its temporary lateral deviation. The described sings (abnormally large muscles, pterygium, deviation to the their side) differentiate this entrapment syndrome from known patterns of the latter. The syndrome was diagnosed in time before the artery was morphologically altered. The surgical treatment involved an extensive resection of the abnormal muscles and revision of the artery.