Which branch of medicine treats patients between the ages of 11 and 21?

The branch of medicine that specifically focuses on treating patients between the ages of 11 and 21 is called Adolescent Medicine. This specialty is designed to address the unique physical, emotional, and social needs of adolescents, recognizing that this developmental stage requires tailored care approaches distinct from other age groups.

Pediatrics typically deals with a broader age range, from infancy through to young adulthood, but does not exclusively focus on the adolescent age group. Geriatrics, on the other hand, specializes in the care of elderly patients, which is entirely different from the adolescent demographic. Therefore, the focus on adolescents as a specific age group sets Adolescent Medicine apart as the correct answer, indicating that it rightly encompasses the treatment of patients aged 11 to 21.