PURPOSE: To assess the impact of socioeconomic position (SEP) over life on a measure of frailty in old age. METHODS: This is a cross-sectional population study of people aged 70 years and more in which 2350 respondents were interviewed in 2008 to 2010. The relationships between different indicators of SEP (childhood standard of living, level of education, occupational class, and current affluence) and quartiles of a frailty index including 43 variables were assessed in ordinal regression models adjusted for potential confounders. RESULTS: Mean age of the population was 83.3 ± 7.5 years, with 59.4% of women. The mean value of the frailty index was 0.19 ± 0.13, with values ranging between 0 and 0.65. All periods of social disadvantage were associated with increasing frailty in bivariate analysis. In multivariate analysis, a poor level financial security in the old age was the SEP indicator the most strongly associated with frailty (odds ratio [OR]: 2.81, 95% confidence interval [CI]: 2.20-3.59), followed by a low level of education (OR: 1.45, 95% CI: 1.17-1.80) and occupation during active life (OR: 1.38, 95% CI: 1.06-1.79). CONCLUSIONS: Socioeconomic inequalities over life affect health capital in old age. The most important risk factor identified in this study, contemporary financial difficulties, was also the most accessible to prevention.