Dementia is a leading cause of death in the developed world. A number of modifiable risk factors for dementia have been identified, yet lay knowledge on dementia risk is limited. A mental models approach was used to compare lay and expert knowledge of risk in order to identify target areas for lay education. This method assumes experts and laypeople use different cognitive representations to make sense of phenomena. Semi-structured interviews were conducted with 8 experts and 15 laypeople to construct mental models of dementia risk. Interviews were transcribed verbatim and entered into NVivo qualitative data analysis software for coding. Findings indicated that laypeople had some knowledge of modifiable risk factors but in contrast to the expert mental model, laypeople poorly understood the causal links between these factors and dementia risk. Lay participants were unsure of the interaction between modifiable and non-modifiable risk factors and primarily attributed dementia risk to “bad luck”. It is suggested that future dementia education could benefit by building upon a general appreciation of healthy behaviour with particular focus on explaining the causal pathways to dementia risk. Additionally, it may be productive to inform laypeople it is possible to “change one’s luck” by engaging in protective behaviours.