Objective: The assessment of behavioral disturbances in amyotrophic lateral sclerosis (ALS) is important because of the overlap with the behavioral variant of frontotemporal dementia (ALS-bvFTD). Motor symptoms and dysarthria are not taken into account in currently used behavioral questionnaires. We examined the clinimetric properties of a new behavioral questionnaire for patients with ALS (Amyotrophic Lateral Sclerosis-Frontotemporal Dementia-Questionnaire [ALS-FTD-Q]). Methods:In addition to other clinimetric properties, we examined reliability, clinical validity, and construct validity of the ALS-FTD-Q, using data from patients with ALS (n ϭ 103), ALS-bvFTD (n ϭ 10), bvFTD (n ϭ 25), muscle disease control subjects (n ϭ 39), and control subjects (n ϭ 31). Construct validity of the ALS-FTD-Q was assessed using the Frontal Systems Behavior scale (FrSBe), Frontal Behavioral Inventory (FBI), Hospital Anxiety and Depression Scale, ALS Functional Rating ScaleϪRevised, Frontal Assessment Battery, Mini-Mental State Examination, and a fluency index. In addition, the point prevalence of behavioral disturbances according to the ALS-FTD-Q was compared with those obtained with the FrSBe and FBI. Results:The internal consistency of the ALS-FTD-Q was good (Cronbach ␣ ϭ 0.92). The ALS-FTD-Q showed construct validity because it correlated highly with other behavioral measures (r ϭ 0.80 and 0.79), moderately with measures of frontal functions and global cognitive functioning (r ϭ 0.37; r ϭ 0.32), and poorly with anxiety/depression and motor impairment (r ϭ 0.18 for both). The ALS-FTD-Q discriminated between patients with ALS-bvFTD, patients with ALS, and control subjects. The point prevalence of behavioral disturbances in patients with ALS measured with the ALS-FTD-Q was lower than that for the FrSBe and FBI.