This paper describes the results of an empirical study about a specific type of error in vocabulary acquisition in French as a second language, that is, intralingual lexical confusion due to formal and/or semantic similarity between target words and other French words known by the learners. Four hundred and eighty English- and Greek-speaking learners (at beginner, intermediate and advanced levels of proficiency in French) were given an L2 to L1 translation task of words with various frequencies. A comparison of the two linguistic groups revealed that the Greeks were more prone to commit errors due to intralinguistic lexical confusion regardless of their level of proficiency in French. Interlinguistic distance seems to have had an impact on these a priori intralingual errors and more specifically on the learners’ ability to distinguish between similar lexical forms in French. Lexical confusion will be discussed from the point of view of the mental lexicon and the strategies that the learners use during lexical identification of written words. The paper will conclude with pedagogical suggestions.