Aim To investigate agreement between: (1) expected reasons and actual reasons for admission of people with dementia according to informal caregivers; (2) scores on measurement instruments prior to admission and the actual reasons for admission according to informal caregivers. Background Timely admission of people with dementia is a crucial issue. Information is highly warranted on whether informal caregivers are capable of prior identification of causes of admission and, can thus be considered a reliable prospective source on causes of admission. Design A cohort study among informal caregivers of people with dementia who made a transition to institutional long-term care. Methods Qualitative data on the expected and actual reasons for admission were collected via open-ended questions at baseline and follow-up. Furthermore, at baseline, data were collected using measurement instruments to measure pre-admission characteristics. Interviews took place between November 2010–April 2012. After categorizing the answers, the agreement between the expected and actual reasons was calculated. Furthermore, bivariate associations were calculated between the actual reasons for admission and scores on corresponding measurement instruments. Results/Findings For most informal caregivers, there was agreement between their statements on the expected reason and the actual reason for admission. A third of the caregivers showed no conformity. Bivariate associations showed that there is also agreement between the actual reasons for admission and scores on corresponding measurement instruments. Conclusion Informal caregivers can be considered reliable sources of information regarding what causes the admission of a person with dementia. Professional care should anticipate informal caregivers’ statements and collaborate with them to strive for timely and appropriate admission.