The authorship of the Theorica planterum has been controversial. According to a medieval tradition, the work was written by Gerard of Cremona. In the (older) scholarly literature (Nallino, Carmody, et al.), however, the work was attributed to Gerard of Sabbioneta. This note reassesses the evidence put forward in support of the authorship of Gerard of Sabbioneta and argues, on the basis of manuscript evidence, that it is highly likely that the Theorica planetarum was translated by Gerard of Cremona or someone from his circle.