This paper explores the possibility that, contrary to the findings of past studies, the L1 and L2mental lexicon may in fact be structurally similar, with depth of individual word knowledgedetermining a given word's degree of integration into the mental lexicon. The paper beginsby reviewing the body of evidence relevant to the research question, and then presents the designand results of an investigation comparing nonnative and native speaker patterns of responses inlight of depth of word knowledge scores. In discussing the results of the study, a tentative modelfor the process by which words are integrated into the mental lexicon is proposed, and thelong-standing belief that a shift from predominantly syntagmatic to predominantly paradigmaticresponses is indicative of lexical development is challenged.