A harmonized classification system for FTLD-TDP pathology has been proposed to replace the two previously used systems. The original studies identified three distinct histological patterns in FTLD-U cases based on the morphology and distribution of ubiquitin immunoreactive neuronal inclusions. Later, TDP-43 was identified as the ubiquitinated pathological protein in most FTLD-U cases, leading to the designation of FTLD-TDP. The two classification systems for FTLD-U/FTLD-TDP have gained wide acceptance but continue to cause confusion due to differing numbering systems. To resolve this, the principal authors of the original studies propose a new classification system using letters to distinguish subtypes, with the order based on relative frequency, avoiding bias. Type A is characterized by numerous short dystrophic neurites and crescentic or oval neuronal cytoplasmic inclusions, primarily in neocortical layer 2. Type B has moderate numbers of neuronal cytoplasmic inclusions throughout all cortical layers. Type C has elongated dystrophic neurites in upper cortical layers. Type D is associated with IBMPFD caused by VCP mutations, characterized by numerous short dystrophic neurites and frequent lentiform neuronal intra-nuclear inclusions. Additional modifications could be considered, but the authors propose no significant changes beyond the coding of subtypes to ensure compatibility with existing systems. The new classification aims to improve communication in FTLD diagnosis and research. The proposal has received unanimous support from all neuropathologists involved in the original studies.A harmonized classification system for FTLD-TDP pathology has been proposed to replace the two previously used systems. The original studies identified three distinct histological patterns in FTLD-U cases based on the morphology and distribution of ubiquitin immunoreactive neuronal inclusions. Later, TDP-43 was identified as the ubiquitinated pathological protein in most FTLD-U cases, leading to the designation of FTLD-TDP. The two classification systems for FTLD-U/FTLD-TDP have gained wide acceptance but continue to cause confusion due to differing numbering systems. To resolve this, the principal authors of the original studies propose a new classification system using letters to distinguish subtypes, with the order based on relative frequency, avoiding bias. Type A is characterized by numerous short dystrophic neurites and crescentic or oval neuronal cytoplasmic inclusions, primarily in neocortical layer 2. Type B has moderate numbers of neuronal cytoplasmic inclusions throughout all cortical layers. Type C has elongated dystrophic neurites in upper cortical layers. Type D is associated with IBMPFD caused by VCP mutations, characterized by numerous short dystrophic neurites and frequent lentiform neuronal intra-nuclear inclusions. Additional modifications could be considered, but the authors propose no significant changes beyond the coding of subtypes to ensure compatibility with existing systems. The new classification aims to improve communication in FTLD diagnosis and research. The proposal has received unanimous support from all neuropathologists involved in the original studies.