<i>Background:</i> Behavioral variant frontotemporal dementia (bvFTD) patients show prefrontal cortex dysfunction and atrophy. <i>Methods:</i> We investigated whether executive function in conjunction with prefrontal cortex atrophy discriminates bvFTD and Alzheimer’s disease (AD) patients efficiently at presentation. <i>Results:</i> AD and bvFTD patients were distinguishable by 89.5% on their performance of 3 executive tasks: the Hayling Test of Inhibitory Control, Digit Span Backward and Letter Fluency. Similarly, scan ratings showed that orbitofrontal cortex (OFC) and dorsolateral prefrontal cortex regions distinguish both patient groups. More importantly, employing the Hayling error score in conjunction with the OFC atrophy rating showed that 92% of patients can be correctly classified into bvFTD and AD. <i>Conclusion:</i> A combination of OFC and disinhibition measures appears to be a powerful diagnostic tool in differentiating bvFTD from AD patients in this preliminary study.