The development of language indicating the emergence of thinking about the thoughts of self and others has been scarcely studied in Spanish-speaking children. For this reason, we studied the development of mental state language and various indicators of language development in 25 Spanish-speaking children assessed at 3, 3inline image, 4, 4inline image, and 5 years of age. We coded and categorized the 40,250 utterances children produced during the five time points, 1202 (3.01%) of which had mental terms. In this sample, mental state language in Spanish children developed with a similar timeline and patterns as described in English-speaking children. However, several findings were novel for studies of mental state language. The general indexes of syntactic development did not correlate with the production of mental terms. The Index of Lexical Diversity was associated with the frequency of references to verbs of desire. The results of regression analyses suggest that not only the development of subordinate sentences with complement is associated with genuine mental references to desires and beliefs, but the development of lexical skills as well.