© 2020 Elsevier Ltd Insufficient sleep has been argued to result in deleterious changes to mood in adolescents and offers promise as a modifiable risk factor. A systematic review of the literature regarding sleep duration and mood in adolescents was conducted using the academic databases PsycINFO, PubMed, Medline, Scopus, and EMBASE to identify relevant literature. Seventy-four studies, including 361,505 adolescents were sourced out of the 1534 references identified, 73 of which were appropriate for meta-analysis. Pooled results indicated that less sleep was associated with a 55% increase in the likelihood of mood deficits. Positive mood showed the largest relationship with sleep duration, followed by anger, depression, negative affect and anxiety. Effect sizes also varied according to study design, how sleep was operationalised, and geographical region, but not according to the inclusion of covariates. Sleep duration has a significant negative impact on a range of mood states in healthy adolescents. These effects were witnessed across all geographical regions, highlighting that sleep is a universal and modifiable risk factor for preventing mood deficits in this at-risk population.