The validation of tau radioligands could improve the diagnosis of frontotemporal lobar degeneration and the assessment of disease-modifying therapies. Here, we demonstrate that binding of the tau radioligand [18F]AV-1451 was significantly abnormal in both magnitude and distribution in a patient with familial frontotemporal dementia due to a MAPT 10 + 16C>T gene mutation, recapitulating the pattern of neuropathology seen in her father. Given the genetic diagnosis and the non-Alzheimer's pathology, these findings suggest that [18F]AV-1451 might be a useful biomarker in primary tauopathies. Largerscale in vivo and post-mortem studies will be needed to assess the technique's specificity.