Chronic recurrent inflammation with joint effusion following anterior cruciate ligament (ACL) reconstruction is common. We report an unusual case of a patient also suffering from undiagnosed Behçet's disease. The patient had chronic recurrent joint effusions of the knee 7 years after traumatic rupture of the ACL and autologous tendon reconstruction using a hamstring tendon autograft. Arthroscopic treatment of the notch impingement and therapy of the accompanying rheumatic disease relieved the patient of his ailment. On the one hand, this case report shows the necessity of including chronic rheumatoid joint disease in the differential diagnosis of a persistent impairment of joint homeostasis following ACL reconstruction, and on the other hand it shows the coincidence of Behçet's disease and recurrent joint inflammation in a patient following ACL surgery.