From the point of view of ecological and attachment theory, professional and non-professional support persons can be an important link between young persons placed in Swedish residential treatment centres (RTC), their families, and staff at the centre. Through interviews with 23 support persons, the aim of the study is to explore characteristics of the relationship between support persons and the young person, and the support persons’ experiences of obstacles to and opportunities for treatment involvement at the facility. The findings show that most support persons describe an emotional relationship with the young person, while a few describe an instrumental one. Most support persons report limited opportunities for treatment involvement, mostly due to facility staff’s non-encouraging attitude, whereas a small group report positive involvement strategies from both staff and social welfare agencies. It is noteworthy that those reporting positive involvement opportunities already have access to the facility because of their professional relation to the residents (e.g. as social welfare officer in charge of the resident’s placement). The importance of staff encouragement of relations between support persons and residents during the RTC placement is discussed.