  The masses and radii of neutron stars are discussed in general relativity and
scalar-tensor theory of gravity and the differences are compared with the
current uncertainties stemming from the nuclear equation of state in the
relativistic mean-field framework. It is shown that astrophysical and
gravitational waves observations of radii of neutron stars with masses $M
\lesssim 1.4 M_{\odot}$ constrain only the nuclear equation of state, and in
particular the density dependence of the nuclear symmetry energy. Future
observations of massive neutron stars may constrain the coupling parameters of
the scalar-tensor theory provided that a general consensus on the dense nuclear
matter equation of state is reached.
