Abstract: A break-in resistant cylinder for locks, comprising a stator provided with a substantially cylindrical longitudinal cavity for accommodating a rotor with a longitudinal recess for the insertion of a key. The rotor and the stator comprise a plurality of channels which are substantially aligned and face each other (when the cylinder is in the closed configuration); the channels accommodate respective coding pins, tumbler pins and any elastic elements designed to prevent the rotation of the rotor within the stator if the key is not present in the longitudinal recess. At least one of the tumbler pins comprises a bush and a spike; the stem of the spike has a smaller diameter than the inside diameter of the bush and is longer than the bush. The spike is arranged so that its head is directed toward the bottom of the channel of the stator and rests against the elastic elements and the free end of the stem rests against the lower surface of the coding pin.