  We discuss the validity, or lack thereof, of the Jebsen-Birkhoff theorem in
scalar-tensor theories by generalizing it and regarding the Brans-Dicke-like
scalar as effective matter. Both the Jordan and Einstein frames are discussed
and an apparent contradiction between static spherical solutions of
scalar-tensor gravity and Hawking's theorem on Brans-Dicke black holes is
clarified. The results are applied to metric and Palatini f(R) gravity.
