According to the projections of the statistical office of the European Union, Eurostat, nearly one third of EU citizens will be at least 65 in 2060. The U.S. population age 65 and older continues to increase and is projected to nearly double from 48 million to 88 million by 2050. Elderly people are especially exposed to neurodegenerative diseases (NDs). The most common ND is Alzheimer's disease (AD), a chronic and progressive disorder with a variety of pathological changes within neuronal tissue, which begin even 10-15 years before the onset of cognitive impairment symptoms. AD is perceived as a disease continuum and considered to include three basic phases: preclinical (asymptomatic) stage, mild cognitive impairment (MCI), and dementia due to AD. A very important issue, from medical and legal perspectives, is the NDs patient's consent to medical procedures, including diagnostic procedures, such as lumber puncture. NDs patients are not always able to express their consent and do not always understand the information provided by a physician. This applies to a group of patients in the final stages of NDs. This paper presents legal regulations of selected European countries and signalizes the U.S. legal solutions on the issue of NDs patients' informed consent to medical procedures.