Localization of excess electrons in sodium chloride clusters is studied using first-principles calculations based on the local-density approximation. In clusters with a rocksaltlike structure containing an anion vacancy, an excess electron was found to localize on an anion vacancy site, in analogy to the bulk F center, stabilizing the structure. Approximately the same degree of localization was found for surface, corner, and interior anion vacancies. For clusters without an anion vacancy, such as Na14Cl13, the excess electron is found to be delocalized over the cluster surface. In contrast to previous theoretical predictions, no tendency is found for the excess electron to localize at a single sodium site, and localization-induced dissociation of a neutral alkali-metal atom is not expected to occur for an isolated cluster.