This article addresses the variation between the Spanish structures 'cuidar (a)' and 'cuidar de', understood as direct and prepositional regimen respectively, from a diachronic perspective. The aim of this study is to demonstrate that a diachronic change that crosses the semantic and syntactic characterization of the verbs cuidar and curar allows explaining the current alternation of cuidar between both structures. The Methodology consisted of the revision of Corpus Diacrónico del Español (CORDE), in order to analyse the direct regimen and prepositional structures of the verbs cuidar and curar, between the 12th and 15th centuries. It was concluded that the semantic transfer from curar to cuidar occurring during the late Middle Ages induces, at the same time, a syntactic change. Namely, it can be said that cuidar begins to admit animated objects in direct regimen constructions, which in the earlier period was only restricted to curar.