Background: to better understand the development of frailty with ageing requires longitudinal studies over an extended time period. Objective: to investigate changes in the degree of frailty during later life, and the extent to which changes are determined by socio-demographic characteristics. Methods: six measurement waves of 1,659 Dutch older adults aged 65 years and over in the Longitudinal Aging Study Amsterdam (LASA) yielded 5,211 observations over 17 years. At each wave, the degree of frailty was measured with a 32-item frailty index (FI), employing the deficit accumulation approach. Socio-demographic characteristics included age, sex, educational level and partner status. Generalized Estimating Equation (GEE) analyses were performed to study longitudinal frailty trajectories. Results: higher baseline FI scores were observed in older people, women, and those with lower education or without partner. The overall mean FI score at baseline was 0.17, and increased to 0.39 after 17 years. The average doubling time in the number of deficits was 12.6 years, and this was similar in those aged 65-74 years and those aged 75+. Partner status was associated with changes over time in FI score, whereas sex and educational level were not. Conclusions: this longitudinal study showed that the degree of frailty increased with ageing, faster than the age-related increase previously observed in cross-sectional studies. Even so, the rate of deficit accumulation was relatively stable during later life.