Amyloid-beta (Abeta) peptide is commonly found in human Alzheimer's disease (AD) brain and is the main component of Alzheimer amyloid plaques. The predominant forms of Abeta in the human brain are Abeta(1-40) and Abeta(1-42), but Abeta(25-35) fragment, physiologically present in elderly people, is the more toxic region and has been recently found to play a relevant role in AD, due to its peculiar aggregation properties. In this work, we review the current understanding on the conformations and biological activity of Abeta(25-35) exploring aggregation, cytotoxic and neurodegenerative properties of this fundamental Abeta fragment, in order to provide an effective starting point to better approach a pathology spread and problematic as AD.