A crucial communication task for unknown brands is to build the knowledge in consumers’ minds necessary to become established. However, communication effectiveness may depend on prior familiarity of the advertised brand. The findings of two experiments using television ads and computer Internet ads revealed that brand familiarity influenced repetition effectiveness. In particular, repetition of advertising attributed to an unfamiliar brand showed decreased effectiveness; when the same advertising was attributed to a known, familiar brand, repetition wearout was postponed. Negative thoughts about tactic inappropriateness were seen to arise with repetition, particularly for an ad for an unfamiliar brand, driving, in part, the decreases in repetition effectiveness.