This article reports on an introspective study that examined the relationship between first language L1; Farsi lexicalization of the concepts represented by the second language L2; English target words and learners' inferencing behavior while reading English texts. Participants were 20 Farsi-speaking university students of English as a foreign language. The results indicate that these learners knew fewer, and inferred meanings for more, nonlexicalized target words than lexicalized words. Although they used similar types and proportions of knowledge sources when inferring meanings for both groups of words, they were far less successful in decoding the meanings of the nonlexicalized words. Lexicalization in the L1 may be one of the factors influencing learners' differential success in L2 text comprehension and vocabulary development.