Background Shunts, the main treatment for hydrocephalus, are problematic as they frequently malfunction. Identifying shunt malfunction requires parents to recognize its symptoms and health professionals to integrate parents' information about the child's symptoms within the clinical assessment to reach a diagnosis. Aim To investigate parent–professional shared decision making during the diagnosis of suspected shunt malfunction in acute hospital admissions. Design and methods A mixed method study involving audio recordings of admission consultations, a shared decision making questionnaire and interviews 1‐week post‐consultation, was undertaken. Twenty‐eight family members and fourteen health professionals participated. The interactions were analysed using conversational analysis, framework approach for the interview data and descriptive statistics for questionnaire responses. Findings Both parents and professionals focussed on establishing a diagnosis and ruling out shunt malfunction when a child with hydrocephalus was ill. Participants' perceived effective collaboration as central to this task: parents wanted to contribute to the process of diagnosis by providing information about the likely cause of symptoms. Professionals were satisfied with the level of involvement by parents, although parent satisfaction was more variable. The challenge for professionals was to integrate parents' expertise of their child's presenting symptoms within clinical decision making processes. Conclusion In this context, both parents' and professionals' perceived their interactions to be about problem‐solving, rather than making decisions about treatments. Although the shared decision‐making model can help patients to make better decisions between treatment options, it is unclear how best to support collaboration between professionals and parents to ensure a good problem‐solving process.