A consensus paper updates the nomenclature and nosology for neuropathologic subtypes of frontotemporal lobar degeneration (FTLD). Previously, FTLD was classified based on the main pathological protein, such as tau (FTLD-tau), TDP-43 (FTLD-TDP), or ubiquitinated inclusions (FTLD-UPS). However, recent findings show that some cases previously classified as FTLD-UPS are actually caused by FUS protein accumulation, leading to the reclassification of these cases as FTLD-FUS. This includes atypical FTLD-U (aFTLD-U), basophilic inclusion body disease (BIBD), and neuronal intermediate filament inclusion disease (NIFID). These three conditions are now grouped under FTLD-FUS due to the prominent role of FUS pathology. It is important to note that this does not imply that FUS is the causative factor in these conditions, but rather that FUS accumulation is the most prominent molecular pathology. Additionally, familial frontotemporal dementia linked to chromosome 3 (FTD-3), caused by mutations in the CHMP2B gene, remains classified as FTLD-UPS because its pathology does not show FUS immunoreactivity. The updated nomenclature now includes three major molecular subgroups: FTLD-tau, FTLD-TDP, and FTLD-FUS. This classification helps in understanding common disease mechanisms, diagnostic tests, and potential treatments. The paper also highlights the importance of identifying the specific pathologic proteins and their relationship to genetic defects. The updated nomenclature provides a logical way to group neuropathologic subtypes and is likely to have relevance for future research and clinical practice.A consensus paper updates the nomenclature and nosology for neuropathologic subtypes of frontotemporal lobar degeneration (FTLD). Previously, FTLD was classified based on the main pathological protein, such as tau (FTLD-tau), TDP-43 (FTLD-TDP), or ubiquitinated inclusions (FTLD-UPS). However, recent findings show that some cases previously classified as FTLD-UPS are actually caused by FUS protein accumulation, leading to the reclassification of these cases as FTLD-FUS. This includes atypical FTLD-U (aFTLD-U), basophilic inclusion body disease (BIBD), and neuronal intermediate filament inclusion disease (NIFID). These three conditions are now grouped under FTLD-FUS due to the prominent role of FUS pathology. It is important to note that this does not imply that FUS is the causative factor in these conditions, but rather that FUS accumulation is the most prominent molecular pathology. Additionally, familial frontotemporal dementia linked to chromosome 3 (FTD-3), caused by mutations in the CHMP2B gene, remains classified as FTLD-UPS because its pathology does not show FUS immunoreactivity. The updated nomenclature now includes three major molecular subgroups: FTLD-tau, FTLD-TDP, and FTLD-FUS. This classification helps in understanding common disease mechanisms, diagnostic tests, and potential treatments. The paper also highlights the importance of identifying the specific pathologic proteins and their relationship to genetic defects. The updated nomenclature provides a logical way to group neuropathologic subtypes and is likely to have relevance for future research and clinical practice.