A standard view of language processing holds that lexical forms are arbitrary, and that non-arbitrary relationships between meaning and form such as onomatopoeias are unusual cases with little relevance to language processing in general. Here we capitalize on the greater extent of iconic lexical forms in a signed language (British Sign Language, BSL), to test how iconic relationships between meaning and form may affect lexical processing. In three experiments, we found that iconicity in BSL facilitated picture-sign matching, phonological decision, and picture naming. In comprehension the effect of iconicity did not interact with other factors, but in production it was observed only for later-learned signs. These findings suggest that iconicity serves to activate conceptual features related to perception and action during lexical processing. We suggest that the same should be true for iconicity in spoken languages (e.g., onomatopoeias), and discuss the implications this has for general theories of lexical processing.