Background <p>Approximately 80% of long-term care residents in Norwegian nursing homes have dementia. Patients with dementia represent a vulnerable group that tends to underreport pain, mainly due to difficulty expressing pain. Nurses are responsible for assessing pain in patients with dementia when signs of discomfort are evident through behavioural changes. Knowledge of the diagnosis and the patient is essential for proper detection and assessment. We aimed to explore nurses’ experiences in assessing pain in patients with dementia in nursing homes.</p> Methods <p>Data were collected through eight individual interviews with nurses at two Norwegian nursing homes in May 2024. To analyse the data, a qualitative design using thematic analysis was conducted following Braun and Clarke’s six steps.</p> Results <p>Three main themes were identified through analysis: (1) pain assessment is similar to detective work; (2) pain assessment of patients with dementia requires collaboration; and (3) nurses’ desire to improve the quality of pain assessment for patients with dementia.</p> Conclusion <p>Pain assessment in people with dementia was described by nurses as a complex process requiring the interpretation of behavioural changes, knowledge of the individual patient, and the integration of information from multiple sources. The findings highlight the importance of clinical reasoning, collaboration, and continuity in supporting pain assessment when self-reports are limited.</p>