Throughout adolescence, both sleep and emotion regulation abilities undergo significant developmental changes. The maturational systems that govern sleep and emotion regulation are closely intertwined leading many researchers to posit a mutually reinforcing relationship. Although there is support for a bidirectional relationship among adults, empirical support for reciprocal relationships among adolescents is lacking. Given the notable developmental changes and instability that occur throughout adolescence, this is a critical period to examine whether sleep and emotion regulation abilities may be reciprocally related. Using a latent curve model with structured residuals, this study examined within-person reciprocal associations between sleep duration and emotion dysregulation among 12,711 Canadian adolescents (Mage = 14.30 years; 50% female). Participants self-reported their sleep duration and emotion dysregulation each year for 3 years beginning in Grade 9. After accounting for underlying developmental trajectories, the results did not support a bidirectional relationship between sleep duration and emotion dysregulation from one year to the next. However, there was evidence of contemporaneous associations between the residuals at each wave of assessment (r = -.12) such that less sleep than expected was concurrently associated with higher-than-expected deviations in emotion dysregulation, or, conversely, that reporting greater emotion dysregulation than expected was associated with lower-than-expected sleep duration. In contrast to previous findings, the between-person associations were not supported. Taken together, these results indicate that the relationship between sleep duration and emotion dysregulation is primarily a within-person process rather than reflecting differences between individuals and likely operates on a more proximal timescale. (PsycInfo Database Record (c) 2023 APA, all rights reserved).