Abstract: A safety closure system for containers acts to discourage children, and the like, from unscrewing a screw-on container cap, either by requiring a positive lock device associated with the cap to be first released, or by confusing the child with misleading opening instructions. The positive lock devices generally include a flap hinged to the cap and provided either with a projection or socket engageable with a mating component provided on the associated container for securing the flap, and thereby the cap, against rotation relative to the container.