Developmental regression is when a child who has reached a certain developmental stage begins to lose previously acquired milestones.[1] It differs from global developmental delay in that a child experiencing developmental delay is either not reaching developmental milestones or not progressing to new developmental milestones, while a child experiencing developmental regression will lose milestones and skills after acquiring them.[2] Developmental regression is associated with diagnoses of autism spectrum disorder,[3] childhood disintegrative disorder,[4] Rett syndrome,[5] Landau-Kleffner syndrome,[6] and neuro-degenerative diseases.[7] The loss of motor, language, and social skills can be treated with occupational therapy,[8] physical therapy,[9] and speech therapy.[10]