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Dorsal root ganglion (DRG) toxicity has been consistently reported as a potential safety concern after delivery of adeno-associated viruses (AAVs) containing gene-replacement vectors but has yet to be reported for RNAi-based vectors. Here, we report DRG toxicity after AAV intra-CSF delivery of an RNAi expression construct-artificial microRNA targeting superoxide dismutase 1 (SOD1)-in non-human primates (NHPs) and provide evidence that this can be recapitulated within mice. Histopathology evaluation showed that NHPs and mice develop DRG toxicity after AAV delivery, including DRG neuron degeneration and necrosis and nerve-fiber degeneration that were associated with increases in cerebrospinal fluid (CSF) and serum phosphorylated neurofilament heavy chain (pNF-H). RNA-sequencing analysis of DRGs showed that dysregulated pathways were preserved between NHPs and mice, including increases in innate/adaptive immune responses and decreases in mitochondrial- and neuronal-related genes, following AAV treatment. Finally, endogenous miR-21-5p was upregulated in DRGs of AAV-treated NHPs and mice. Increases in miR-21-5p were also identified within the CSF of NHPs, which significantly correlated with pNF-H, implicating miR-21-5p as a potential biomarker of DRG toxicity in conjunction with other molecular analytes. This work highlights the importance of assessing safety concerns related to DRG toxicity when developing RNAi-based AAV vectors for therapeutic purposes., Competing Interests: Declaration of interests M.L.H. is a paid advisor from Charter Preclinical Services. All other authors are or were paid employees at Biogen., (Copyright © 2024 The American Society of Gene and Cell Therapy. Published by Elsevier Inc. All rights reserved.)