  The Higgs boson spectrum of the Next-to-Minimal Supersymmetric Standard Model
is examined. The model includes a singlet Higgs field S in addition to the two
Higgs doublets of the minimal extension. `Natural' values of the parameters of
the model are motivated by their renormalization group running and the vacuum
stability. The qualitative features of the Higgs boson masses are dependent on
how strongly the Peccei-Quinn U(1) symmetry of the model is broken, measured by
the self-coupling of the singlet field in the superpotential. We explore the
Higgs boson masses and their couplings to gauge bosons for various
representative scenarios.
