The sucking reflex does not exist in normal adults, but can reappear when there are pathologic changes in the central nervous system. The sucking reflex is one of the primitive reflexes that appear in newborns after birth. The sucking reflex is an important sign that the infant is developing normal neurologic function, and it usually disappears after 3 months, making it difficult to observe clinically. This is mainly because these primitive reflexes are suppressed at the central horizontal level (cerebral cortex and pyramidal fasciculus) with growth and development. When a pathological condition exists in the central nervous system, the sucking reflex may reappear. This is often seen in patients with Alzheimer’s disease. The primitive reflex tends to reappear with age, after degenerative brain lesions and cognitive decline. A 6-month follow-up study in Japan showed the presence of the sucking reflex in 28 (23.1%) elderly people in whom there was a significant reduction in cognitive function. However, the exact association and cause of central nervous system lesions and the primitive reflex is still under investigation. In conclusion, the sucking reflex does not occur in normal adults, but if it is found in adults (elderly), one should be alerted to the presence of central nervous system lesions and seek medical attention to avoid delays.