The mapping of lexical form to meaning is an important part of vocabulary acquisition in a second language (L2). This study examines the proposition that L2 lexical forms are often mapped to the existing semantic content of their first language (L1) translations rather than to new semantic specifications of their own. Native and nonnative English speakers were asked to perform two semantic judgment tasks in which they had to determine the degree of semantic relatedness of English word pairs (experiment 1) or to decide whether two English words were related in meaning (experiment 2). The nonnative speakers, but not the native speakers, were found to provide higher rating scores on or responded faster to L2 word pairs sharing the same L1 translations than to L2 word pairs that do not. The finding is interpreted as strong evidence in support of the presence of L1 semantic content in L2 lexical entries.