Sleep duration has received considerable attention as a potential risk factor of suicidality in youths; however, evidence on the dose–response association between sleep duration and suicidality has not been synthesized. This meta-analysis examined linear and nonlinear dose–response relationships between sleep duration and the risk of suicidality in adolescents and explored potential moderators of the associations. Electronic databases, namely EMBASE, PubMed, PsycINFO, ProQuest Dissertations & Theses A&I Wanfang Data (Chinese database), and the China Knowledge Resource Integrated Database, were searched from their inception to April 18, 2017. Studies examining the association between sleep duration and suicidality in adolescents were included. A random-effects dose–response model was used to estimate the linear and nonlinear dose–response relationships. We identified 13 reports that included a total of 598,281 participants for a systematic review, and 12 reports were further used for a dose–response meta-analysis. Strong curvilinear dose–response associations were obtained for both suicidal ideation and attempts, with the lowest suicidal ideation and attempt risks at sleep durations of 8 h and 8–9 h per day (all P_nonlinearity < 0.001). A linear dose–response relationship between sleep duration and suicide plans (pooled OR = 0.89, 95% confidence interval [CI] = 0.88–0.90) was obtained, indicating that the risk of suicide plans statistically decreased by 11% for every 1-h increase in sleep duration. Depression did not moderate the association between sleep duration and suicidality in youths. Our findings suggest curvilinear dose–response associations between sleep duration and the risks of suicidal ideation and attempts and a linear dose–response relationship between sleep duration and suicide plan risk. Additional longitudinal studies are warranted to establish causality.