Intrauterine gene therapy (IUGT) potentially enables the treatment and possible cure of monogenic -diseases that cause severe fetal damage. The main benefits of this approach will be the ability to correct the disorder before the onset of irreversible pathology and inducing central immune tolerance to the vector and transgene if treatment is instituted in early gestation. Cure has been demonstrated in small animal models, but because of the significant differences in immune ontogeny and the much shorter gestation compared to humans, it is unlikely that questions of long-term efficacy and safety will be adequately addressed in rodents. The nonhuman primate (NHP) allows investigation of key issues, in particular, the different outcomes in early and late-gestation IUGT associated with different stages of immune maturity, longevity of transgene expression, and delayed-onset adverse events in treated offspring and mothers including insertional mutagenesis. Here, we describe a model based on the Macaca fascicularis using ultrasound and fetoscopic approaches to systemic vector delivery and the processes involved in vector administration and longitudinal analyses.