We tested a cue-based retrieval model that predicts how similarity between discourse entities influences the speaker's choice of referring expressions. In Experiment 1, speakers produced fewer pronouns (relative to repeated noun phrases) when the competitor was in the same situation as the referent (both on a horse) rather than in a different situation (only the referent on a horse). The situational congruence had a larger impact when it was relevant to the to-be-described action (getting off a horse) than otherwise (taking off a hat), suggesting that the effect of similarity is modulated by its relevance to other conceptual representations held by the speaker. Experiment 2 found an effect of the competitor's similarity regardless of whether pronouns were ambiguous or not, suggesting that the effect is independent of ambiguity avoidance and results from speaker-internal production constraints. (Contains 6 figures.)