The objective of this study was to evaluate the first language (L1) vocabulary knowledge in a large-scale sample (n = 70) of second-generation Russian-Jewish immigrants in Israel. The interest in this research population follows from the unique demographic, sociocultural, linguistic, and psychological distinctiveness of RJ immigration in Israel. The study focused on the question of whether the L1 vocabulary knowledge of second-generation children is restrictive compared with their second language (L2) vocabulary and, if so, in what way. A within-subjects design was used to compare the participants' performance on lexical knowledge tests in Russian (L1) and Hebrew (L2). The comparison of expressive lexical knowledge in L1 and L2 of Russian-Hebrew speaking children on an array of measures clearly shows L2 dominance. The researchers conclude, therefore, that second-generation children who receive their educational instruction in a non-additive L2 context do not perform better in L1 than in L2 in tasks requiring deep lexical knowledge. (Contains 7 tables.)