Background The rapid increase of frail older people worldwide will have a substantial impact on healthcare systems. The frailty process may be delayed or even reversed, which makes it attractive for early interventions. However, little is known about the determinants of frailty state changes. The aim of this study is to compare socio-demographic determinants of worsening in frailty state in 11 European countries. Methods Data of 14 424 community-dwelling persons aged >= 55 years, enrolled in 2004 in the Survey of Health, Ageing and Retirement in Europe, were analysed. Three frailty states were identified (non-frail, pre-frail and frail) using Fried's criteria, and frailty state changes over a 2-year period were determined. Multinomial regression analyses adjusted for baseline frailty state were conducted to investigate whether sex, age, marital status and level of education determined a worsening in frai Results Of all individuals, 22.1% worsened, 61.8% showed no change and 16.1% improved in frailty state. Women, those aged >= 65 years, and lower educated persons showed an increased risk of worsening in frailty state. In Southern European countries, there was an earlier and larger increase in risk of worsening in frailty state in life, which was more pronounced in women compared with men. Conclusions In Europe, persons aged >= 65 years, women and lower educated persons are at increased risk of worsening in frailty state. Differences between countries indicate that interventions aimed at delaying the frailty process in Southern European countries should start earlier with more attention towards women.