We characterize the ω-stable theories all of whose
countable models admit decidable presentations. In particular, we show that for
a countable ω-stable T, every
countable model of T admits a decidable presentation if and
only if all n-types in T are recursive and
T has only countably many countable models. We further
characterize the decidable models of ω-stable
theories with countably many countable models as those which realize only
recursive types.