The validity of the Fundación MacArthur Inventario del Desarrollo de Habilidades Comunicativas: Palabras y Enunciados (IDHC:PE) was examined with twenty 20- and nineteen 28-month-old, typically developing, monolingual, Spanish-speaking children living in Mexico. One measure of vocabulary (number of words) and two measures of grammar (mean of the three longest utterances and grammatical complexity score) from the IDHC:PE were compared to behavioral measures of vocabulary (number of different words from a language sample and number of objects named in a confrontation naming task) and one behavioral measure of grammar (mean length of utterance from a language sample). Only vocabulary measures were assessed in the 20-month-olds because of floor effects on the grammar measures. Results indicated validity for assessing expressive vocabulary in 20-month-olds and expressive vocabulary and grammar in 28-month-olds.