Many genetic metabolic diseases manifest in infancy, therefore, it is important to develop effective treatments that could be implemented at this time. Adeno-associated virus serotype 8 (AAV8) gene transfer has been studied in neonatal mouse, cat, and dog models and shown some efficacy with a single hepatic injection at birth. AAV8-mediated liver gene transfer has also generated sustained therapeutic effects in feline and canine models of lysosomal storage disorders. In these models, delaying the age of vector treatment increased gene transfer stability. The growth rate of infant nonhuman primates is more similar to the growth trajectory of humans, thus infant monkeys provide an excellent model to study AAV gene transfer efficiency, stability, and safety. In this study, we report for the first time that AAV8-mediated hepatic gene transfer in infant monkeys is safe and efficient but less stable when compared to adolescent animals. Infant monkeys administered AAV8 intravenously at 1 week postnatal age achieved up to 98% transduction of hepatocytes within 7 days of injection; however, there was significant dilution of genomes and loss of transgene expression 35 days postadministration. Delaying the injection to 1 month postnatal age did not improve stability of transduction but decreased the antibody response to AAV8 capsid.