Financial errors by patients with dementia can have devastating personal and family consequences. We developed and evaluated a neuroeconomic conceptual framework for understanding financial errors across different dementia syndromes, using a systematic, retrospective, blinded chart review of demographically-balanced cohorts of patients with Alzheimer's disease (AD, n=100) and behavioral variant frontotemporal dementia (bvFTD, n=50). Reviewers recorded specific reports of financial errors according to a conceptual framework identifying patient cognitive and affective characteristics, and contextual influences, conferring susceptibility to each error. Specific financial errors were reported for 49% of AD and 70% of bvFTD patients (p = 0.012). AD patients were more likely than bvFTD patients to make amnestic errors (p < 0.001), while bvFTD patients were more likely to spend excessively (p = 0.004) and to exhibit other behaviors consistent with diminished sensitivity to losses and other negative outcomes (p < 0.001). Exploratory factor analysis identified a social/affective vulnerability factor associated with errors in bvFTD, and a cognitive vulnerability factor associated with errors in AD. Our findings highlight the frequency and functional importance of financial errors as symptoms of AD and bvFTD. A conceptual model derived from neuroeconomic literature identifies factors that influence vulnerability to different types of financial error in different dementia syndromes, with implications for early diagnosis and subsequent risk prevention.