There is a documented and often unmet need for interventions aimed at supporting young people with attention-deficit/hyperactivity disorder (ADHD) and/or autism spectrum disorder (ASD) in their transition between adolescence and adulthood. Difficulties with social interaction, initiation difficulties, and impairments in executive function can complicate visits at a clinic, i.e. traditional treatment, for individuals with neuropsychiatric disorders (NPD). A model for internet-based support and coaching aimed at young people with ASD and/or ADHD was developed and tested at three treatment sites in western Sweden. The implementation was analyzed against an inventory according to which implementations are more likely to be successful if an intervention: 1) has advantages compared to other existing methods, 2) matches the individual and organizational values, norms and work practices of its recipients, 3) is perceived as easy to use, and 4) is adaptable to local conditions and the recipients' needs. Data were collected through group interviews with professionals involved in the implementation of the intervention. The implementation of the intervention showed promising results on measures such as access, delivery/quality of healthcare services, and equality of distribution of healthcare services. The identified impediments to successful implementation related to a wide range of factors and levels, including the design of the intervention, technical issues, attitudes of staff, organizational culture, and organizational structure at the implementation sites in terms of patient stock, work division, and resource allocation. The results are consistent with previous studies that stress the need for multi-component implementation strategies.