OBJECTIVES: This article aimed to assess associations of childhood socioeconomic conditions (CSC) with the risk of frailty in old age and whether adulthood socioeconomic conditions (ASC) influence this association. METHODS: Data from 21,185 individuals aged 50 years and older included in the longitudinal Survey of Health, Ageing, and Retirement in Europe were used. Frailty was operationalized as a sum of presenting weakness, shrinking, exhaustion, slowness, or low activity. Confounder-adjusted multilevel logistic regression models were used to analyze associations of CSC and ASC with frailty. RESULTS: While disadvantaged CSC was associated with higher odds of (pre-)frailty in women and men (odds ratio [OR] = 1.73, 95% confidence interval [CI] 1.34, 2.24; OR = 1.84, 95% CI 1.27, 2.66, respectively), this association was mediated by ASC. Personal factors and demographics, such as birth cohort, chronic conditions, and difficulties with activities of daily living, increased the odds of being (pre-)frail. DISCUSSION: Findings suggest that CSC are associated with frailty at old age. However, when taking into account ASC, this association no longer persists. The results show the importance of improving socioeconomic conditions over the whole life course in order to reduce health inequalities in old age.