Background: Facilitating adult sibling involvement for individuals with pervasive support needs is important. This study explores the attitudes of healthcare professionals in this process. Method: The attitudes of healthcare professionals (n = 60) in the Netherlands were explored through an online, self-developed survey with open and closed-ended questions. Results: Around 40% of the participants reported (partly) lacking knowledge about sibling preferences and 23% (partly) lacking practical opportunities for involving siblings. The majority (partly) perceived the involvement of siblings as an enjoyable part of their work (82%), rated their knowledge and skills positively (87%), and regarded sibling involvement as such importance that they would be willing to exert considerable effort to contribute to it (61%). Not all participants perceived it as their job to collaborate with siblings. Conclusions: There is a need to increase healthcare professionals' knowledge about adult sibling preferences and structurally embed sibling involvement within care practices.