A surgical ring, designed to be implanted around biological organs comprising a pouch or a duct, so as, on the one hand, to form a closed loop between these two extremities (1, 2), thus forming a first (1) and a second (2) extremity and, on the other hand, to reduce the diameter of the opening of the organ when it is tightened by the ring, the ring including a system for reversibly controlling the variation in its diameter. The system also includes a flexible filiform element (4), inserted longitudinally with possibility of sliding into the material constituting the body of the ring between the first (1) and second (2) extremities, so as to define a fixed portion (5) connected to the first extremity (1) and a free portion (7) associated with an actuator (8) mounted on the ring near the second extremity (2).