Introduction:Client-accessible interdisciplinary health records potentially contribute to integrated care by facilitating collaboration and enhancing clients’ involvement in care. To achieve this, three Dutch organizations providing ‘care for youth’ developed a fully client-accessible electronic patient record (EPR-Youth).Objective:To evaluate the implementation of EPR-Youth and to determine barriers and facilitators.Methods:A mixed methods design combined system data, process observations, questionnaires and focus group interviews. Target groups were parents, adolescents, professionals using EPR-Youth, and implementation stakeholders.Findings:Client-portal acceptability was high among all clients. Client-portal adoption rate was high and differed between age groups and educational levels. Professionals’ doubts about acceptability, appropriateness and fidelity were partly due to lack of system knowledge. Implementation barriers were the complexity of co-creation, lack of clear leadership, and concerns about legal issues. Facilitators were clarifying vision and legal context, setting deadlines, and a pioneering spirit.Conclusion:The early implementation of EPR-Youth, the first Dutch client-accessible interdisciplinary electronic health record in ‘care for youth’ was successful. To enhance adoption among clients, group-specific barriers for portal-use should be determined. Professionals need additional training. Further research is needed to gain insight into client-portal access barriers. To benefit more from co-creation, an organizational change towards situational leadership is necessary.