let $g$ be a finite subgroup of su(2) or so(3). mckay correspondence describes the classical geometry of g-hilb (the hilbert scheme of $g$-clusters in $c^2$ or $c^3$) in terms of the representation theory of $g$. we determine the gromov-witten invariants of $g$-hilb and describe it in terms of a root system canonically associated to $g$. this in particular describes the quantum cohomology of $g$-hilb in terms of the associated root system.