A readily evaluated condition for migration dynamic recrystallization is developed. It is based on the postulate that “the distance traversed by the boundary of a hypothetical growing grain in the time taken for the attainment of a recovery steady state must exceed the size of a critical nucleus”. A method for estimating the boundary mobility based on the kinetics of static recrystallization is also developed to facilitate evaluation of the condition. The derivation focuses first on developing an upper limit for the dynamically recrystallized grain size. This upper limit is only slightly higher than experimental values. The critical condition also agrees well with a limited set of experimental data. These data include the occurrence (and, in two cases, suppression) of dynamic recrystallization in Cu, Ni, Mg, α-Fe, γ-Fe and Al.