Background: Differential diagnosis between frontotemporal dementia (FTD) and Alzheimer's disease (AD) is often challenging. Autopsy series have identified AD pathology in a consistent percentage of patients clinically diagnosed with frontotemporal dementia (FTD). It has been demonstrated that the levels of tau and Aβ42 in cerebrospinal fluid (CSF) are a reliable marker for AD. Objective: To evaluate the presence of a CSF AD-like pattern in patients with FTD, and the related brain changes, to assess whether these patients had features resembling an AD pattern of hypoperfusion. Methods: Clinically-diagnosed non-monogenic FTD patients underwent an extensive neuropsychological assessment, 99mTc-ECD SPECT, and CSF analysis (tau and Aβ42 levels). FTD AD-like and FTD non-AD-like patterns were identified, and neuropsychological and neuroimaging features compared. Results: CSF AD-like pattern was reported in 9 cases out of 43 (21%). FTD AD-like and non-AD-like patients did not differ in demographic characteristics, cognitive deficits, or behavioral changes. Both groups had greater hypoperfusion in frontotemporal lobes as compared to age-matched controls. When FTD AD-like patients were compared to the FTD non-AD-like group, the former had greater hypoperfusion in brain areas typically affected by AD, namely precuneus, temporal, and parietal areas. Conclusions: CSF AD-like profile in FTD is associated with brain abnormalities typically found in classical AD, confirming the usefulness of CSF testing. Detecting an ongoing AD pathological process in FTD has several implications for defining distinctive treatment approaches, guiding genetic screening, and helping in patient selection in future clinical trials in both FTLD and AD therapeutics.