It has been suggested that olfactory perception relies on a memory-based pattern-matching system. In this experiment, we tested a prediction derived from this approach, namely that representations of unfamiliar odors are less stable than those of familiar odors. Participants provided qualitative descriptions of odors either immediately after smelling them or after a 1- or 3-min delay. Later, participants were given a surprise test in which they were asked to match their earlier descriptions to those same odors. Delay exerted no effect on familiar odors. However, for unfamiliar odors, while their matching performance was equivalent to that for familiar odors when descriptions were made immediately, delay significantly impaired performance. The better capacity to name familiar odors only assisted matching performance at the longest (3-min) delay. These findings suggest that unfamiliar odors have less stable representations than do familiar odors. Pattern-matching theory suggests that this occurs because unfamiliar odors weakly activate many nodes in memory, resulting in less-stable percepts.