Socially inappropriate behavior accompanies and modulates delinquency across the lifespan. In contrast to young people, the emergence of such traits among older individuals could indicate incipient neurodegenerative disease. Before developing a neurocognitive disorder, subtle behavioral changes may reflect a disintegration of neural networks involved in impulse control or social cognition. Whereas psychiatric evaluation often considers a comprehensive cognitive assessment, unremarkable results may discourage clinicians from recognizing brain disease underlying behavioral disturbance. We first provide an overview of its manifestations and neural correlates and the interrelations with mild cognitive impairment (MCI) before demonstrating how to investigate and diagnose mild behavioral impairment (MBI). Finally, we show how to appreciate MBI in geriatric forensic psychiatry.