This paper explores the trade-off between cognitive effort and cognitive effects during immediate metaphor comprehension. We specifically evaluate the fundamental claim of relevance theory that metaphor understanding, like all utterance interpretation, is constrained by the presumption of optimal relevance (Sperber and Wilson, 1995, p. 270): the ostensive stimulus is relevant enough for it to be worth the addressee's effort to process it, and the ostensive stimulus is the most relevant one compatible with the communicator's abilities and preferences. One important implication (...) of optimal relevance is that listeners follow a path of least effort and stop processing at the first interpretation that satisfies their expectation of relevance. They do this by trying to minimize cognitive effort while maximizing cognitive effects. Some relevance theory scholars suggest that metaphors should require additional cognitive effort to be understood, and that in return they yield more cognitive effects than does literal speech. Others claim that metaphors may be understood quickly, as soon as people infer enough effects for the speaker's utterance to meet their expectation of optimal relevance. Our analysis of the experimental evidence suggests that there is no systematic relationship between cognitive effort and cognitive effects in metaphor comprehension. We conclude that relevance theory need not make any general predictions about the effort needed to comprehend metaphors. Nevertheless, relevance theory is consistent with many of the findings in psycholinguistics on metaphor understanding, and can account for aspects of metaphor understanding that no other theory can explain. (shrink)