Let G be a group and let pi(e)(G) be the element orders set of G. For
any subset Gamma of positive integers let h(Gamma) be the number of is
omorphic classes of group G satisfying pi(e)(G) = Gamma. If G is finit
e, it is proved that h(Gamma) is an element of {1, 2} for some orthogo
nal groups M where Gamma = pi(e)(M).