BACKGROUND: Frailty is an important risk factor for adverse outcomes in older people. Substantial variation in frailty prevalence between socioeconomic groups exists, but longitudinal evidence for the association between socioeconomic position (SEP) and frailty is scarce. OBJECTIVE: To investigate the course of socioeconomic inequalities in frailty among older adults during 10 years of follow-up. METHODS: Data were used from the Longitudinal Aging Study Amsterdam (n = 1,509). Frailty was measured with the functional domains approach, based on deficiencies in four domains: physical, nutritive, cognitive, and sensory. Mixed-model analyses were performed to estimate the course of frailty and its association with SEP during a 10-year follow-up. We investigated whether similar patterns of associations held in different scenarios, comparing results of survivor analyses with those based on two imputation methods accounting for dropout due to death (substitution of first missing value and missing values imputed with a prediction model). RESULTS: All scenarios showed a linear increase in frailty with aging (survivor analyses OR = 1.87, 95% CI = 1.66-2.11) and associations of low education and low income with frailty (adjusted OR for low education = 1.76, 95% CI = 1.05-2.97; adjusted OR for low income = 1.90, 95% CI = 1.20-3.01; both for survivor analyses). Sex-stratified analyses indicated that socioeconomic inequalities were mainly present in men, not in women. Similar patterns of associations of SEP with frailty were observed in all scenarios, but the increase in frailty prevalence over time differed substantially between the scenarios. There were no statistically significant interactions between time and SEP on frailty (all scenarios), suggesting that inequalities in frailty did not increase or decrease during follow-up. CONCLUSION: SEP inequalities in frailty among older adults were observed, mainly among men, and persisted during 10 years of follow-up.