  We present an n-ary constraint for the stable marriage problem. This
constraint acts between two sets of integer variables where the domains of
those variables represent preferences. Our constraint enforces stability and
disallows bigamy. For a stable marriage instance with $n$ men and $n$ women we
require only one of these constraints, and the complexity of enforcing
arc-consistency is $O(n^2)$ which is optimal in the size of input. Our
computational studies show that our n-ary constraint is significantly faster
and more space efficient than the encodings presented in \cite{cp01}. We also
introduce a new problem to the constraint community, the sex-equal stable
marriage problem.
