Research on individual differences in second language (L2) reading ability has primarily focused on factors known to contribute to first language (L1) reading ability, with little consideration of factors mediating interference between languages. In an exploratory analysis, we compared the degree to which the linguistic interference that readers experience predicted reading ability in L1 and L2. Based on current psycholinguistic models, we also investigated whether the relation is mediated by working memory capacity. A series of regression analyses were performed to investigate these relations in 83 monolinguals, 50 L1 English-speaking bilinguals, and 127 L2 English-speaking bilinguals. Results revealed that the amount of linguistic interference experienced significantly predicted reading ability in L2 but not in L1 or for monolinguals. Further, the relation was not mediated by individual differences in working memory capacity. These results illustrate the need for consideration of cross-linguistic factors for models of L2 reading ability in particular.