This paper concerns preconditions for the well-being of young people with mental ill-health combined with social vulnerabilities, also referred to as youth with complex needs. Research questions are: What barriers to sustainable work practices for young people labelled as having complex needs do professionals encounter? What do professionals identify as possible ways to overcome these barriers? Sustainable work practices are reflected in three themes: empowerment, relationships and collaboration. The findings are based on semi-structured interviews with 24 professionals, 3 men and 21 women, working in psychiatric care and the social services in two Swedish municipalities in 2016 and 2017. Major barriers are lack of continuity and co-ordination in staff and support, and fragmentation of work practices. As a consequence of the increased specialization of human service organizations, young people have to interact with many different professionals which could cause disparate interventions. Possible ways mentioned to overcome these barriers are supported through good interactional skills, using keyworkers as well therapeutic alliances, wrap-around services and case management. Complexity is linked to organizations and work practices rather than to young people. An often dysfunctional service delivery system in organizations with rigid boundaries may also affect professionals' aim for sustainable support.