This paper describes a syndrome of entrap ment of the infrapatellar branch of the saphe nous nerve attributable to its anatomical rela tionship to the sartorius muscle and justifies its identification as a distinct entity. Surgery was performed on four knees in three pa tients for localized pain and tenderness. The infrapatellar nerve was found entrapped be hind the sartorius tendon against the promi nent edge of the medial femoral condyle and sharply angulated while passing around the sartorius in two knees. Entrapment during passage of the nerve through a slit in the musculotendinous portion of the sartorius was observed in the others. All patients had complete relief of symptoms after transloca tion of the nerve away from the site of entrap ment. The characteristic findings demon strate the need to be aware of the possibility of entrapment of the infrapatellar branch of the saphenous nerve when evaluating pa tients with pain on the medial aspect of the knee.