Sandhoff disease is a heritable lysosomal storage disease resulting from impaired degradation of G_M2 ganglioside and related substrates. A mouse model of Sandhoff disease created by gene targeting displays progressive neurological manifestations, similar to patients with the disease. In the present in vivo and in vitro studies, we examined morphological and functional abnormalities of dorsal root ganglion (DRG) neurones in Sandhoff disease mice at an asymptomatic stage (approximately 1 month of age). Light microscopic studies with Nissl staining and immunocytochemistry suggested extensive intracytoplasmic storage of G_M2 ganglioside in the Sandhoff mouse DRG neurones. These findings were consistent with the results of electron microscopy, in which a huge number of pleomorphic inclusion bodies immunoreactive for G_M2 ganglioside were present in the cytoplasm of the neurones. The inclusion bodies were also identified in satellite cells and Schwann cells in the Sandhoff mouse DRG. The survival ratios of DRG neurones after 1, 2, 4 and 6 days in culture were significantly lower in the Sandhoff mice than in the age‐matched heterozygous mice. The ratio of neurite‐bearing cells on poly‐l‐lysine‐coated dishes after 2 days in culture was also lower by approximately 10% in the Sandhoff mice compared to the heterozygotes, but additional coating of laminin onto poly‐l‐lysine dramatically enhanced the neurite extension from the neurones in both groups of mice. These results indicate that accumulation of G_M2 ganglioside in DRG neurones impairs the capability of the neurones to survive in vitro, although viable neurones from the Sandhoff mice in culture can regenerate neurites nearly as well as unaffected neurones.