Aging is a primary risk factor for both neurodegenerative disorders (NDs) and tumors such as adult‐onset brain tumors. Since NDs and tumors are severe, disabling, progressive and often incurable conditions, they represent a pressing problem in terms of human suffering and economic costs to the healthcare systems. The current challenge for physicians and researchers is to develop new therapeutic strategies in both areas to improve the patients’ quality of life. In addition to genetics and environmental stressors, the increase in cellular oxidative stress as one of the potential common etiologies has been reported for both disorders. Recently, the scientific community has focused on the beneficial effects of dietary antioxidant classes, known as nutraceuticals, such as carotenoids, vitamins, and polyphenols. Among these compounds, polyphenols are considered to be one of the most bioactive agents in neurodegeneration and tumor prevention. Despite the beneficial activity of polyphenols, their poor bioavailability and inefficient delivery systems are the main factors limiting their use in medicine and functional food. The development of polymeric nanoparticle‐based delivery systems able to encapsulate and preserve polyphenolic compounds may represent a promising tool to enhance their stability, solubility, and cell membrane permeation. In the present review we provide an overview of the main polyphenolic compounds used for ND and brain tumor prevention and treatment that explores their mechanisms of action, recent clinical findings and principal factors limiting their application in medicine. NDs and tumors are severe, disabling, progressive, and often incurable conditions, and represent a pressing problem in terms of human suffering and economic costs to the healthcare systems. Recently, the scientific community has focused on the beneficial effects of dietary antioxidant classes, such as polyphenols, in neurodegeneration and tumor prevention. Pre‐clinical and clinical evidence shows that polyphenolic compounds are safe and able to interact in synergy with commonly used therapeutic treatment.