A container for transporting a receptacle (2) containing a radioactive substance for medical use. includes a shielded body made up of a belt of side walls connected to a base element and defining a top opening, and a shielded closing lid attachable to the top opening by locking elements shaped so as to be activated by a translational movement of the lid in the top opening, this “locking movement” taking place along the axis of the opening and towards the opposing base element. The lid is further equipped with elements for deactivating the locking elements to enable it to be separated from the container body. In one advantageous embodiment, the lid has a plurality of retractable projecting studs designed to fit by a snap-action type phenomenon into at least one complementary housing formed in the opening of the container body during the locking movement.