The deltoid or medial collateral ligament consisting of superficial and deep components together with the spring ligament is the primary stabilizer of the ankle joint. Injuries of these anatomical structures are more frequent than assumed but are nevertheless often overlooked. Inadequate treatment can lead to chronic pain, instability, hindfoot deformities and ankle arthritis. Patient history and clinical assessment can help to identify injuries of the deltoid ligament. Magnetic resonance imaging (MRI) is the diagnostic method of choice. Arthroscopy of the ankle joint can be a valuable tool in the assessment of the injury. Treatment should include accompanying injuries and deformities and can range from immobilization in a cast to ligament repair up to ligament reconstruction using a free tendon graft.