Translation equivalents (TEs) characterize the lexicon of bilinguals from the early stages of acquisition, as reported in studies involving English and other languages in which most cross-language synonyms are dissimilar in phonological form. This research explores the emergence of TEs in Spanish-Catalan bilinguals who are acquiring two languages with many cognate words and thus languages with many cross-language synonyms with identical or similar phonological forms. Expressive vocabulary was obtained in two 18-month-old groups (monolingual and bilingual, N = 24 each) through parental report using a bilingual questionnaire. Four different vocabulary size measures were computed in bilinguals, correcting for different types of phonological overlap in words across their two languages. Bilinguals were found comparable to monolinguals in every measure except for Total Vocabulary Size (Spanish + Catalan words) in which they outscored monolinguals due to the high number of form-identical cross-language elements in their expressive vocabularies. Form-similar and dissimilar TEs accounted for less than 2% of the words produced and were only present in infants with larger vocabularies. Results support the hypothesis that phonological form proximity between words across bilinguals' two languages facilitates early lexical acquisition.