PROJECT SUMMARY The Childhood Development after Cochlear Implantation (CDaCI) Study is a multisite, prospective investigation of a large, diverse cohort of US children with cochlear implants (CIs). Participants were originally enrolled and implanted between 2002 and 2004 at six pediatric CI centers. The participants include children with severe-to- profound sensorineural hearing loss who received a CI before 5 years of age (n=188) and a control group (n=97) of normally hearing age-mates. Uniquely, we have utilized a “whole child” approach to examine outcomes, including: (a) audiology and speech recognition; (b) spoken language and speech production; (c) parent-child interactions and cognitive, behavioral, and social functioning; and (d) quality of life (QoL) and health utility. Success with CIs depends on complex interactions between multiple domains of development. Accordingly, the aims are driven by hypotheses that relate variability in post-CI performance to environmental, social, interventional, and biological influences. This multidimensional study offers great potential for novel, generalizable insights into sources of variation in communicative, social, and behavioral development that affect long-term outcomes. The CDaCI Study concludes with this final submission as the CI participants reach emerging adulthood. Final data collection will assess outcomes related to attainment of independence and adult roles, socioemotional functioning, and QoL through the administration of online surveys. These assessments target relevant challenges encountered through the post-high school experience and identify daily life factors that affect the CI recipients' capacity to enter college, the workplace, and live independently. We also will be able to calculate the cost-effectiveness of this surgical intervention. The CDaCI Study is in the exclusive position to track 20 years of developmental outcomes stemming from early childhood to adolescence, through emerging adulthood. In this submission, the following five aims are addressed: (I) To examine the achievement of adult roles and independence, psychosocial functioning, and HRQoL in a national cohort of adolescents and young adults who received a CI by 5 years of age; (II) To evaluate the lifetime societal costs and burden of severe-to-profound hearing loss and determine the cost utility of CIs over at least 15 years of follow-up; (III) To evaluate the psychometric properties of our new, CI-specific HRQoL measure for adolescents and emerging adults; (IV) To identify duration of CI use and intervention choices that facilitate achieving normal verbal and academic levels, and to examine the relationship between communication skill attainment and young adult outcomes; and, (V) To compile a master database longitudinally linking data across the entire study period and release a de-identified public-use dataset of the CDaCI data collected from 2002-2022.