World Alzheimer's Day is observed on September 21 to raise awareness about Alzheimer's disease and dementia. First observed in 1994, it is organised by Alzheimer's Disease International (ADI). Alzheimer's is the most common cause of dementia and mainly impairs memory and thinking. The day encourages early diagnosis, caregiver support and dementia awareness, and seeks to reduce stigma. The 2026 theme is “The Earlier You Know, The More You Can Do: A Dementia Diagnosis Matters.”