Diabetes mellitus (one of the most common endocrine disorders) and dementia are two of the most prevalent conditions affecting ageing individuals. The fact that type 2 diabetes is a risk factor for dementia became evident around 15 years ago, and now we also know that type 1 diabetes is associated with brain dysfunction. Questions still remain whether diabetes is a causal risk factor for dementia, or is merely a coexisting condition. If the former were true, it raises the interesting hypothesis that treating diabetes, its features, or its complications may reduce the risk of future dementia. In my presentation, I will present data from previous and ongoing observational studies in people at different stages of ageing, to provide insights into the complex relationship between diabetes and dementia and contextualise their findings to other work in the field.