Abstract: An electromechanical cylinder lock-key combination includes a cylinder housing and a cylinder core rotatably arranged in the cylinder housing and having a key-way for receiving a key. A plurality of key actuated moveable blocking elements block the rotation of the cylinder core unless a correct key is inserted in the key-way. An optical code reader in the lock reads an optical code element provided on an inserted key. At least one of said blocking elements functions as a bar element barring insertion of the key into the key-way unless a correct optical code element is provided on the key. By using at least one of the mechanical elements already present in the lock as part of the electronically controlled blocking mechanism, in combination with the use of an optical code requiring no moveable parts for the reading thereof, space requirements in the lock device are kept to a minimum.