CSF NFL levels are higher in all FTD subgroups compared with HCs, AD patients, presymptomatic carriers of FTD mutations, and PD patients. CSF NFL in all FTD subgroups correlates moderately with CDR-SB (r = 0.359). CSF NFL has moderate negative correlations with MMSE score (r = -0.549) and with the performance in several neuropsychological tests (mostly of frontal-executive functions). In FTD and bvFTD, CSF NFL levels correlate negatively with gray matter volume of frontal, temporal, parietal, occipital, and cingulate cortices and, to a lesser extent, with volume of associated white matter. Here, NEFL is linked to Alzheimer disease.