Jolan Walter, MD, PhD, division chief of the University of South Florida (USF) and Johns Hopkins All Children’s Pediatric Allergy & Immunology Programs, discusses the importance of long-term follow-up after treatment for severe combined immunodeficiency (SCID), which is a life-threatening primary immunodeficiency that is typically diagnosed at birth. Early detection, infection prevention, and early treatment are critical for these children so that most may be able to develop their own working immune system. Dr. Walter indicates that bone marrow recovery and reconstitution should be happening in the first 3 weeks.