Diagnosis of Alzheimer's disease is by clinical and neuropsychological examination, and the presence of deficits in at least two areas of cognition, with progressive worsening of memory. Alzheimer's disease is most likely to be the sum of external factors, such as environmental triggers, and inherent host factors, resulting from genetic predisposition. The children of a person with an affected gene have a 50 per cent chance of inheriting the gene. It does not skip generations and men and women are equally affected.

Increasingly, evidence suggests that Alzheimer's disease is related to lifestyle choices. Other risk factors include head injuries, which can trigger neurodegeneration; epilepsy; herpes zoster and simplex viruses; alcohol; smoking; cardiovascular and cerebrovascular disease, and older maternal age.