Purpose: This study examined the nature of the relation between language-specific vocabulary and conceptual lexical-semantic skills with grammatical abilities within and across languages in preschool Latino dual language learners (DLLs). Method: Sixty-one typically developing, Spanish-English speaking DLLs from preschools serving low-income families participated in the study. Lexical, semantic, and grammar skills were assessed toward the end of the fall in both Spanish and English using normative and researcher-developed assessment instruments. Hierarchical linear regressions using baseline cross-sectional data were completed to determine the association of language-specific vocabulary and bilingual lexical and semantic abilities to grammatical skills measured by sentence repetition tasks in Spanish and English both within and across languages. Results: Results from the study revealed that a considerable percentage of the variance in the grammatical ability of these Latino DLL preschoolers in both Spanish and English was explained by lexical variables in the same language (54% in English and 16% in Spanish). In the strong language (Spanish), bilingual semantic skills also played a role, explaining an additional 8% of the variance. Conceptual vocabulary was a significant predictor of English grammar in the model that excluded the language-specific vocabulary measures. Conclusions: These findings suggest that grammatical skills in the Latino preschoolers examined in the study are strongly related to language-specific measures of vocabulary. In contrast, no evidence supporting the relation between vocabulary and grammar skills across languages was observed. Findings from this study provide insight into the impact of bilingual lexical-semantic knowledge on the grammatical skills of dual-language preschool children developing language abilities in their 2 languages. Clinical implications are also discussed.