IntroductionDespite interventions by low and middle-income countries toward the achievement of the global Sustainable Development Goal (SDG) on promoting mental health and well-being of their populace by the year 2030, suicidal behaviours continue to be major causes of premature mortality, especially among young people. This study examined the prevalence and predictors of suicidal behaviours among in-school adolescents in Mozambique.Materials and methodsThis was a cross-sectional study of 1918 in-school adolescents using data from the 2015 Global School-based Health Survey (GSHS) of Mozambique. The outcome variables (suicidal ideation, suicidal plan, and suicidal attempt) were measured with single items in the survey. Both bivariate and multivariate analyses were performed using chi-square test of independence and binary logistic regression respectively. Results are presented as Adjusted Odds Ratios for the binary logistic regression analysis. Statistical significance was set at p<0.05.ResultsThe prevalence of suicidal behaviours 12 months prior to the survey were 17.7%, 19.6% and 18.5% for suicidal ideation, suicidal plan, and suicidal attempt respectively. Adolescents who experienced anxiety had higher odds of suicidal ideation [AOR = 1.616, 95%CI = 1.148–2.275], suicidal plan [AOR = 1.507, 95%CI = 1.077–2.108], and suicidal attempt [AOR = 1.740, 95%CI = 1.228–2.467]. Adolescents who were physically attacked in school were also more likely to ideate [AOR = 1.463, 95%CI = 1.115–1.921], plan [AOR = 1.328, 95%CI = 1.020–1.728], and attempt [AOR = 1.701, 95%CI = 1.306–2.215] suicide. Having close friends was, however, an important protective factor against suicidal ideation [AOR = 0.694, 95%CI = 0.496–0.971], plan [AOR = 0.625, 95%CI = 0.455–0.860], and attempt [AOR = 0.529, 95%CI = 0.384–0.729]. Peer support also reduced the risk of suicidal ideation [AOR = 0.704, 95%CI = 0.538,0.920] and plan [AOR = 0.743, 95%CI = 0.572,0.966] among the in-school adolescents.ConclusionSuicidal behaviours constitute major public health challenges among in-school adolescents in Mozambique. The behaviours are predominant among adolescents who are physically attacked and those who experience anxiety. Conversely, having close friends serves as a protective factor against suicidal behaviours. To ensure that Mozambique meets the SDG target of promoting the mental health of all by the year 2030, the Government of Mozambique and educational authorities should urgently design and implement innovative interventions and strengthen existing ones that seek to address physical attacks and anxiety among in-school adolescents. School administrations should also incorporate programmes that seek to congregate students and offer platforms for social interaction and cohesion.