This study reports evidence of cross-linguistic influence in possessive constructions in the speech of an English-Spanish simultaneous bilingual child between ages 2;3 and 5;6. Although in English possessives might be pre-nominal ('-s), they might also be post-nominal (of possessives); the latter realization of the possessive is restricted to certain semantic contexts. In contrast, possession is always post-nominal in Spanish. Unlike the monolingual child English data and the English parental speech which revealed mostly instances of the pre-nominal possessive (only 3% in the child data), the bilingual child produced post-nominal possessives in 33% of his English possessives. Similarly, though the monolingual child Spanish data revealed no non-target-like forms, the bilingual child produced a significant number of pre-nominal possessives (e.g.' de las cabritas mama'), which is never grammatical in Spanish. The non-target-like forms found in the bilingual child data strongly suggest evidence of influence of Spanish onto English as well as influence of English onto Spanish.