Abstract Individuals with Down syndrome (DS) are predisposed to OSAS due to craniofacial features (midface hypoplasia, glossoptosis) and studies have shown that the prevalence of OSAS in this population is markedly increased compared to that of typically developing children. Adenotonsillectomy (AT) is considered first-line treatment for childhood OSAS. However, OSAS resolves in only a portion of children with DS after AT. In fact, many children with DS are referred for positive airway pressure (PAP) therapy initiation due to persistent OSAS after AT, and PAP appears to be an important feature of the experience of living with DS. PAP has been shown to be highly effective at treating OSAS and improve OSAS-associated neurobehavioral symptoms, such as quality of life, behavior, mood, daytime sleepiness and school performance. However, PAP as a treatment for OSAS has not been well-studied in children with DS. Therefore, we propose to leverage the HEalthy SLeeP for Children with Down Syndrome (HELP-DS, U01HL125295-S1 and U01HL123507-S1) infrastructure and conduct in two HELP-DS sites (Philadelphia and Cincinnati) plus the University of Miami, a randomized controlled trial to test a 6-month intensive behavioral intervention (INT) to improve PAP adherence vs standard clinical care (CON). Participants with DS and OSAS, aged 6-17.9 years, referred to PAP initiation for the treatment of OSAS will be included. They will undergo standardized evaluations of quality of life, behavior, attention, and family-relevant outcomes, PAP adherence, and health care utilization at baseline, 6, and 12 months. This rigorous design and comprehensive study will resolve existing uncertainties on initial management approaches for children with DS and OSAS treated with PAP by addressing critical issues: a) determine the efficacy of INT vs CON in promoting PAP adherence, b) elucidate which factors mediate or moderate adherence to PAP in children with DS and OSAS, c) determine the effect of PAP use on neurobehavioral and family-relevant outcomes, and quality of life.