Frailty and sleep disturbances are two major concerns in late adulthood, that not only profoundly threaten health and wellbeing at the individual level but place enormous demands on our healthcare systems. Given that both constructs represent dynamic states that are preventable and reversible, understanding the potential pathways to and effects of these variables on one another is critical in providing effective and tailored support. However, despite growing interest in the relationship between sleep and frailty, only one study to date has directly explored their potential bidirectionality. Accordingly, this study was designed to extend the current understanding by investigating the reciprocal relationship of frailty and sleep quality at the multidimensional level. Specifically, the bidirectionality of these relationships was considered separately for physical, psychological, cognitive, and social frailty. Four random-intercept cross-lagged panel models with three time points were conducted, using 3192 older adults (M