Gene transfer into hematopoietic stem cells (HSCs) using integrating vectors is an attractive treatment strategy for many genetic and hematological diseases. The preclinical testing of gene transfer approaches in non-human primates and other large animal models will be invaluable in order to assess toxicity and efficacy, as their HSC biology is much more closely related to humans than murine models. Gene transfer studies targeting HSCs in non-human primates have focused on optimizing gene transfer efficiency, and significant advances have been achieved using standard retroviral vectors. Utilization of lentiviral and other alternative vector system are still very preliminary in large animal models. Further development of post-transduction selection and/or expansion strategies using drug-resistance or amplifier genes will most likely be necessary for clinical applications.