Background: A limited number of studies have analyzed grammaticality in monolingual Spanish-speaking children with specific language impairment (SLI). Most of the available data are based on bilingual speakers. Aims: To extend previous studies by doing a more detailed analysis of grammatical types in monolingual Spanish-speakers with and without SLI. Methods & Procedures: Forty-nine Spanish-speaking children (18 with SLI, 17 age-matched typically developing controls, 14 language-matched controls) were recruited from schools in Mexico and observed in a spontaneous narrative task. Outcomes & Results: The findings were inconsistent with those of previous studies. Significant differences were found for article, connector and preposition omissions, and the per cent of ungrammatical utterances. There were no significant differences found for clitics and verb phrases, though clitic substitutions were frequent. Language-matched controls did not produce different frequencies of ungrammatical utterances. Conclusions & Implications: Significant differences were found for three main items: the per cent of ungrammatical utterances, the omission of articles and the omission of prepositions. Therefore, we propose these components be taken into consideration when distinguishing typically developing children from children with SLI.