AbstractMethylenetetrahydrofolate reductase (MTHFR) mutations have been linked to many diseases. Evidence has been provided to prove that we need to perform pharmacogenetic studies regarding the prevalence of MTHFR mutations and diseases, risks, and the impact on folate requirement in general, but little has been published about Puerto Ricans. A multi center cross-sectional retrospective review study or a prospective pharmacogenetic study of valid genotypes and phenotypes of MTHFR mutations within the different populations of Puerto Ricans and Hispanics are recommended, because differences within them and within the general population are expected.