This study investigated primary and secondary morphological family size effects in monolingual and bilingual processing, combining experimentation with computational modeling. Family size effects were investigated in an English lexical decision task for Dutch-English bilinguals and English monolinguals using the same materials. To account for the possibility that family size effects may only show up in words that resemble words in the native language of the bilinguals, the materials included, in addition to purely English items, Dutch-English cognates (identical and non-identical in form). As expected, the monolingual data revealed facilitatory effects of English primary family size. Moreover, while the monolingual data did not show a main effect of cognate status, only form-identical cognates revealed an inhibitory effect of English secondary family size. The bilingual data showed stronger facilitation for identical cognates, but as for monolinguals, this effect was attenuated for words with a large secondary family size. In all, the Dutch-English primary and secondary family size effects in bilinguals were strikingly similar to those of monolinguals. Computational simulations suggest that the primary and secondary family size effects can be understood in terms of discriminative learning of the English lexicon. (C) 2014 Elsevier Inc. All rights reserved.