The present study focuses on organizations delivering services to individuals with intellectual disability, where trust relations between professionals and family members are required. More specifically, we examine the existence of significant differences in the degree to which family members and professionals trust each other. We also propose that their joint participation in collaborative teams (VI) will improve trust (VD). Specifically, our teams (experimental condition) designed and implemented collaborative projects with the participation of professionals and family members. Participants in the control condition did not participate in the collaborative projects. Our results confirmed that family members trust professionals more than professionals trust family members. Their joint participation in collaborative projects improved professionals' trust in family members over time, compared to the control condition. The effect of collaborative projects was not significant for family members' trust in professionals.