Proactive Health Support (PaHS) is a large-scale intervention in Denmark carried out by registered nurses (RNs) who provide self-management support to people at risk of hospital admission to enhance their health, coping, and quality of life. PaHS is initiated with a face-to-face session followed by telephone conversations. We aimed to explore the start-up sessions, including if and how the relationship between participants and RNs developed at the onset of PaHS. We used an ethnographic design including observations and informal interviews. Data were analyzed using a phenomenological–hermeneutical approach. The study showed that contexts such as hospitals and RNs legitimized the intervention. Face-to-face communication contributed to credibility, just as the same RN throughout the intervention ensured continuity. We conclude that start-up sessions before telephone-based self-management support enable a trust-based relationship between participants and RNs. Continuous contact with the same RNs throughout the session promoted participation in the intervention.