Abstract: An extension stop removably mountable on a polycentric hinge for limiting the forward pivotal rotation of a pair of rigid arms pivotally connected by the hinge. The hinge is of the type wherein a pair of rigid arms are connected at spaced-apart pivotal connections between a pair of parallel face plates. Intermeshing gear teeth are provided on the mating ends of the arms so as to cause simultaneous pivotal action of both arms about their pivotal connections with the plates. The extension stop is a C-shaped plastic body which is attachable along one of the face plates. The stop includes a resilient clip for attaching the stop to one of the face plates and an extension block at the opposing end positionable between the mating ends of the arms to limit the forward rotation of the arms. The extension stop is made of a strong, lightweight plastic. Different size block means are provided to allow the user to select the limit of extension.