Ageing, genetic, medical and lifestyle factors contribute to the risk of Alzheimer’s disease and other dementias. Around a third of dementia cases are attributable to modifiable risk factors such as physical inactivity, smoking and hypertension. With the rising prevalence and lack of neuroprotective drugs, there is renewed focus on dementia prevention strategies across the lifespan. Neurologists encounter many people with risk factors for dementia and are frequently asked whether lifestyle changes may help. Exercise has emerged as a key intervention for influencing cognition positively, including reducing the risk of age-related cognitive decline and dementia. This article focuses on the current evidence for physical inactivity as a modifiable dementia risk factor and aims to support neurologists when discussing risk reduction.