BACKGROUND: The rising prevalence of multi-morbidity increases treatment complexity and caregiving demands, often necessitating involvement of family members as informal caregivers. While essential, this involvement can be burdensome, causing distress for family members. Shared decision-making facilitates communication and supports the alignment of patients' and families' preferences and needs with care and treatment decisions. Involving family during patient hospitalisation can be essential as the whole family is affected by illness. AIM: This project aimed to develop and test a decision aid to systematise family involvement during patient hospitalisation. RESEARCH METHODS: The project was based on the theoretical framework of family nursing, and the Danish Patient Decision Aid template guided the process. The decision options, pros and cons were based on 22 patient and 16 family interviews, which were thematically analysed. Six patients, two family members and nine healthcare professionals alpha tested the decision-aid prototype, which was later beta tested in real-life clinical settings at five internal medical wards. FINDINGS: Three themes emerged: (A) 'involving family when needed', (B) 'waiting for ward rounds' and (C) 'involving family with technology', informing the decision-aid prototype which consisted of five option cards: (1) 'I will involve my family myself', (2) 'I do not want to involve my family', (3) 'Family wants to be present physically', (4) 'Family wants to participate by phone' and (5) 'Family wants to participate by video'. The cards included pros/cons of each option. Alpha testing showed high acceptability and usability, and no alterations were made to the prototype. CONCLUSION: The structured patient decision aid enabled a systematic approach to involve the patient's family. It facilitated meaningful conversations between healthcare professionals, patients and family members. The decision aid identified and addressed patients' and family members' specific needs and preferences during hospitalisation.