A head restraint assembly is provided with a first guide member mounted proximate to a vehicle seat back. A second guide member is mounted to the first guide member for translation along the first guide member. A locking mechanism is mounted to the second guide member in cooperation with the first guide member for locking the second guide member relative to the first guide member. The first and second guide members are the only guide members to minimize binding. The locking mechanism includes a torsion spring connected to the first guide member and oriented about the second guide member for locking the second guide member relative to the first guide member. A lever is mounted to the torsion spring for unlocking the torsion spring.