A thin, elastic circular ring constrained in a rigid cavity is subjected to a uniformly distributed parallel loading per unit length of the ring in its plane. Stability of equilibrium in the large (snap-through) is investigated. This nonlinear problem is simplified by considering the region of separation of the ring at buckling to be small, an assumption supported by experiments. This restriction permits the construction of simple expressions for the dependence of the load on the deformation, for the load at buckling, and for other relevant quantities at and beyond buckling.