Immigrant populations are growing and permanently changing the demographic profile of the United States. Diverse cultural and linguistic backgrounds are imposing demands and challenges upon agencies serving young children and families. Culturally sensitive assessments are not always available for these populations, and psychometric properties of available instruments have not always been investigated. This study examined one developmental screening instrument translated and adapted for Spanish-speaking families, the "Ages and Stages Questionnaires, Third Edition," and evaluated how scores of children on the 9-, 18-, and 30-month Spanish translation differed from scores of children on the English version of the "Ages and Stages Questionnaires, Third Edition." Item characteristics across the English and Spanish versions of the "Ages and Stages Questionnaires, Third Edition," were investigated. Findings indicated that most of the "Ages and Stages Questionnaires, Third Edition," items functioned invariantly across language versions, indicating that these items were productive for gathering information, presented an adequate hierarchy difficulty for order of items, and were eliciting a range of response options included on the tool. Implications for practice and research are discussed, supporting cross-cultural studies on parent-completed questionnaires as necessary for effective screening and monitoring of young children's development in a context of cultural and linguistic diversity.