The 43-kD transactive response (TAR)-DNA-binding protein (TARDBP) mutations have been demonstrated to be causative of sporadic and familial forms of amyotrophic lateral sclerosis. More recently, these mutations have been reported in cases of frontotemporal lobar degeneration (FTLD). The aim of this study was to evaluate the role of TARDBP genetic variations in a large sample of consecutive patients with FTLD. A total of 252 FTLD patients were investigated. Each subject had a clinical and neuropsychological evaluation and a brain imaging study. The clinical diagnosis was confirmed by at least 1 year of follow up. The entire TARDBP gene, the intronic flaking regions, and the 5'-untranslated region (5'-UTR) were screened. Six genetic variations were identified in patients with behavioral variant frontotemporal dementia (FTD) and FTD with motor neuron disease phenotypes. Two of these mutations, namely N267S and M359V, lead to amino acid changes within exon 6. We further identified three genetic variations, i.e., Y214Y, IVS-IV + 45C/T, and 5'-UTR G/A, that could potentially affect the normal splicing process as predicted by in silico analyses. None of these genetic variations was found in healthy age-matched controls. Moreover, we identified a previously described benign variant, A66A, in 5 patients. Our study has confirmed and extended the list of pathogenetic mutations in the TARDBP gene in both apparently sporadic and familial FTLD patients. This work further supports the need for TARDBP screening in FTLD. Also intronic splicing that affects mutations should be considered as well.