Significance Primary stem cells are difficult to transfect, and their viability and function are impaired by traditional transfection methods. We show that nanostraws can be used to deliver RNA to primary human hematopoietic stem cells without any detectable negative effects. Nanostraw-treated cells show no alterations in gene expression and fully retain their proliferative capacity and their potential to regenerate blood cells of different lineages in vivo. This nonperturbative transfection method can benefit functional studies and clinical applications where minimal impact on stem cell function and viability is required.