Vitamin B12 deficiency is a condition resulting from inadequate levels of vitamin B12, essential for red blood cell formation, neurological function, and DNA synthesis. Clinically, it can lead to megaloblastic anaemia and neurological disorders, making early diagnosis crucial to prevent irreversible damage. A key association is pernicious anaemia, an autoimmune condition that impairs vitamin B12 absorption, highlighting the importance of understanding underlying causes in patient management.