Objective: Our aim was to compare the frequency of criminal conduct in patients with behavioral variant frontotemporal dementia (bvFTD), semantic dementia (SD), and Alzheimer disease.Background: A few small-scale studies of antisocial and criminal behavior in patients with frontotemporal lobar degeneration have focused on the clinical subtype bvFTD. It is not yet known whether antisocial behavior affects patients with other clinical subtypes of frontotemporal lobar degeneration, like SD, and patients with other dementing disorders, like Alzheimer disease.Methods: We used a standardized caregiver interview to assess criminal behavior in 83 outpatients: 32 with bvFTD, 18 with SD, and 33 with Alzheimer disease.Results: We found criminal behavior (theft, willful damage to property, housebreaking, assault, or indecent behavior) in 54% of the patients with bvFTD and 56% of those with SD, but only 12% of those with Alzheimer disease.Conclusions: Just over half of our patients with bvFTD or SD had committed crimes. When middle-aged or older patients commit minor crimes, frontotemporal lobar degeneration should be considered as a possible cause. If an affected person faces criminal charges, the court might take incapability or diminished responsibility into account in reaching a verdict.