Using the method of centre stage diagramming, this 3-year [2007–2009] longitudinal study reports a single case study of Ben and Mary that maps the onset of Alzheimer's disease within Ben's late-stage Parkinson's disease and the impact, adjustment and meaning that this had for the couple. It is believed that that this is the first time that such a transition has been documented within a qualitative research design. The importance of Ben and Mary obtaining a diagnosis of Alzheimer's disease is reported as the diagnosis helped to locate the meaning of Ben's memory and behavioural changes within a ‘dementia’ context, rather than as an extension of late-onset Parkinson's disease as was originally considered by the couple. Ben and Mary's search for stability within their life once the diagnosis of Alzheimer's disease was made is also shared. The couple was recruited from the caseload of a Parkinson's disease nurse specialist in North Wales and the couple was visited five times over the duration of the study. All interviews were conducted in Ben and Mary's own home and with their full involvement in the development and reporting of each centre stage diagram. Policy and practice implications are also considered.