Risk factors associated with admission of people with dementia to long-term care institutions need to be identified to support health-care professionals in dementia care at home. An explorative study, combining quantitative and qualitative data collection methods, was performed in people with dementia in Spain. The sample, consisting of people with dementia receiving formal care from health-care professionals but at risk of institutionalisation, and their informal care-givers; and people with dementia recently admitted to a long-term care institution, and their informal care-givers, was interviewed between November 2010 and April 2012. Perceived reasons for admission were determined through an open-ended question put to both groups. Presumed risk factors were collected with validated questionnaires and analysed using bivariate analysis. A total of 287 people with dementia and informal care-givers were studied. Reasons given by the institutionalised group were mostly related to the level of dependency of the person with dementia. People recently admitted to a long-term care institution had more cognitive impairment, a greater degree of dependency and poorer quality of life than those still living at home. Home-care services in Spain need to develop or improve interventions based on the risk factors identified in this study: informal care-giver profile, high cognitive impairment, high level of dependency and the poor quality of life of the person with dementia.