Data on how body mass index (BMI), waist circumference (WC) and waist-to-hip ratio (WHR) are associated with body fat in the oldest-old people are scarce. The purpose of this study was to examine if BMI, WC or WHR are associated with leptin, a biological surrogate measure of body fat in 90-year-old people. The data comes from the Vitality 90+ Study, a prospective population-based study of people living in Tampere, Finland. BMI, WC, WHR and plasma concentration of leptin were available for 160 women and 54 men aged 90 years. BMI and WC had a strong significant positive association with leptin both in women and in men, but WHR was associated with leptin only in men. In conclusion, based on the circulating level of leptin, BMI and WC, and WHR in men, reflect body fat in 90-year-old people, but WHR seems to be a poor indicator of body fat in 90-year-old women.