Because the aetiology of Alzheimer's disease (AD) remains unclear, and fasting hyperinsulinaemia has been incriminated in several human diseases, we examined the relationship between AD, fasting plasma insulin, glucose, body mass index and waist: hip ratio in 24 men and 24 women aged 58–90 years of whom half had probable AD. AD patients were randomly selected from the Bristol Memory Disorders Clinic, while controls were chosen from patients' spouses and the local community. Women with AD, compared with controls, have higher plasma insulin (p = 0.04), higher glucose (p = 0.04), and higher body mass index (p — 0.01). Similar differences were present in men but were not statistically significant except for body mass index (p = 0.03). We conclude that patients with AD have hyperinsulinaemia and insulin resistance, and this may be secondary to being overweight but a causal relationship cannot be excluded.