The article is an empirical study on the position of reflexive pronouns in modal periphrases with infinitive in Spanish and Catalan.The corpus (N=3 588), composed of 10 pairs of syntactic oppositions in both languages, represents scientific discourse.The research question was the position of the reflexive pronoun in relation to the infinitive (e.g., se puede decir vs. puede decirse) and possible differences between Spanish and Catalan.Regarding Spanish, the results confirm that the pre-infinitival placement of reflexive pronouns is frequent in scientific texts, despite being associated with oral language.Furthermore, the results show a high degree of homogeneity between both syntactic variants.The results for Catalan, by contrast, show statistically significant differences both between the different cases analysed and with regard to Spanish.Catalan tends to prefer the pre-infinitival placement of reflexive pronouns, but when a modal verb is used with a personal subject, their distribution is much more even.