In Löfgren's syndrome, pain and swelling commonly involves the ankle joints. In this prospective case series, the magnetic resonance imaging findings of ankle joint involvement are described. Extensive subcutaneous and soft tissue oedema was commonly seen around the ankles. Bone, cartilage, ligaments and tendons were typically uninvolved. Small amounts of joint and tenosynovial fluid were present without evidence of synovial thickening or synovitis. The fluid is probably reactive to adjacent inflammation in the para-articular soft tissues and probably not representing a primary site of involvement. These findings demonstrate that the arthritis in Löfgren's syndrome stems primarily from periarthritis. This is consistent with prior descriptions using ultrasonography.