<b><i>Background:</i></b> Mutations in the genes encoding the heterogeneous nuclear ribonucleoproteins hnRNPA1 and hnRNPA2/B1 have been reported in a multisystem proteinopathy that includes amyotrophic lateral sclerosis (ALS) and inclusion body myopathy associated with Paget disease of the bone and frontotemporal dementia. Mutations were also described in the prion-like domain of hnRNPA1 in patients with classic ALS. Another hnRNP protein, hnRNPA3, has been found to be associated with the ALS/frontotemporal dementia protein C9orf72. <b><i>Objective:</i></b> To further assess their role in ALS, we examined these hnRNPs in spinal cord tissue from sporadic (SALS) and familial ALS (FALS) patients, including <i>C9orf72</i> repeat expansion-positive patients, and controls. We also sought to determine the prevalence of <i>HNRNPA1</i>, <i>HNRNPA2B1,</i> and <i>HNRNPA3</i> mutations in Australian ALS patients. <b><i>Methods:</i></b> Immunostaining was used to assess hnRNPs in ALS patient spinal cords. Mutation analysis of the <i>HNRNPA1</i>, <i>HNRNPA2B1,</i> and <i>HNRNPA3 </i>genes was performed in FALS and of their prion-like domains in SALS patients. <b><i>Results:</i></b> Immunostaining of spinal motor neurons of ALS patients with the <i>C9orf72</i> repeat expansion showed significant mislocalisation of hnRNPA3, and no differences in hnRNPA1 or A2/B1 localisation, compared to controls. No novel or known mutations were identified in <i>HNRNPA1</i>, <i>HNRNPA2B1,</i> or <i>HNRNPA3</i> in Australian ALS patients. <b><i>Conclusions:</i></b> hnRNPA3 pathology was identified in motor neurons of ALS patients with<i> C9orf72</i> repeat expansions, implicating hnRNPA3 in the pathogenesis of <i>C9orf72</i>-linked ALS. hnRNPA3 warrants further investigation into the pathogenesis of ALS linked to <i>C9orf72</i>. This study also determined that <i>HNRNP</i> mutations are not a common cause of FALS and SALS in Australia.