AbstractIn this paper we approach the problem of establishing stability conditions for adaptive controllers from a different perspective: namely, we are interested in knowing when a controller structure that minimizes a linear quadratic criterion can be adaptively implemented to ensure global stability. The main result is the proof that, for systems of relative degree zero, controller structures that solve the linear quadratic optimal control (LQOC) problem1are globally stable when the parameters are adaptively updated. Interestingly enough, no positive realness or matchability assumption is required to establish the result.