To explore the construct validity of the Spanish version of the Frontal Systems Behavioral Scale (FrSBe) using Rasch modelling. Methods: Item responses of 245 Spanish subjects were analysed using Rasch analysis: self-rating of 65 participants with TBI or stroke (sample A), family-rating of the same 65 participants (sample B) and self-rating of 115 healthy individuals (sample C). Results: After removing or grouping several problematic items, the Apathy and the Executive Dysfunction sub-scales were found to be valid measures for samples A and B and the Disinhibition sub-scale was valid for samples B and C. Person Separation Index of reliability of sub-scales was greater than 0.83 for sample B and 0.72 for A and C. All items showed disordered threshold categories in samples A and B and five items were ordered in sample C. Conclusions: With a few modifications, the sub-scales of the FrSBe-Spanish version are adequate measures for the assessment of the behavioural syndromes derived from frontal systems dysfunction in persons with brain injury. The family-rating form is preferable to the self-rating form. Only the Disinhibition scale is a valid measure for the behavioural assessment of the normal population. A reduction of response categories is suggested.