A collapsible firearm butt-stock assembly has a shoulder stock 18 coupled with a pair of guide rods 20, 22 slideable in respective guide holes 14, 16 of a housing 12. A locking mechanism including locking members engageable with guide rod recesses 26, 28 provided in the guide rods has an actuator 30 that is movable in the lengthways direction of the guide rods to release the locking members to allow sliding movement of the shoulder stock relative to the housing.