{\L}ojasiewicz ideals in Denjoy-Carleman classes

The classical notion of {\L}ojasiewicz ideals of smooth functions is studied in the context of non-quasianalytic Denjoy-Carleman classes. In the case of principal ideals, we obtain a characterization of {\L}ojasiewicz ideals in terms of properties of a generator. This characterization involves a certain type of estimates that differ from the usual {\L}ojasiewicz inequality. We then show that basic properties of {\L}ojasiewicz ideals in the ${\mathcal{C}}^{\mathrm{\infty }}$ case have a Denjoy-Carleman counterpart.