In this study, we investigate whether specific language impairment (SLI) manifests itself grammatically in the same way in Spanish and English with respect to nominal plural marking. English-speaking children with SLI are very proficient at marking plural on nouns. Spanish has two main nominal plural allomorphs: /s/ and /es/. The /es/ allomorph has received multiple theoretical treatments, including one (e.g., Harris (1991)) which argues that in singular-plural pairs such as "flor-flores," the /e/ is epenthetic, while other accounts (e.g., Colina (2003)) argue that synchronically there is an underlying /e/ in the singular form (e.g., "flore") which gets deleted by apocope. Child Spanish speakers with SLI in the United States have shown mixed results in their abilities to learn plural marking. They have shown low proficiency on an elicited production task, but have shown high proficiency in spontaneous production data. We show, using a new elicited production task in Mexico with a group of children diagnosed with SLI and two control groups, that performance is close to the high levels previously shown in spontaneous production studies. Further, we show that all children's performance with the epenthetic allomorph /es/ is worse than their performance with the canonical allomorph /s/. Our results suggest that plural marking is not an axis of cross-linguistic variation between Spanish and English among children with SLI. On the basis of the absence of child errors of the "flore" type and presence of errors of the "flors" type, our data appear to support the epenthesis account of Harris (1991). (Contains 2 figures, 5 footnotes and 8 tables.)