Background Disparities in involuntary psychiatric hospitalisation between population subgroups have been identified in adults, but little is known about the factors associated with involuntary hospitalisation in children or adolescents. We did a systematic review, meta-analysis, and narrative synthesis to investigate the social and clinical factors associated with involuntary psychiatric hospitalisation among children and adolescents.Methods We searched MEDLINE, PsycINFO, Embase, and the Cochrane Central Register of Controlled Trials for studies of any type up to July 22, 2020, that compared the characteristics of voluntary and involuntary psychiatric inpatients (mean age of sample ≤18 years). We synthesised results using random effects meta-analysis on unadjusted data and by narrative synthesis. Heterogeneity between studies was calculated using I². This study is registered on PROSPERO, CRD42020099892.Findings 23 studies from 11 countries were included in the systematic review and narrative synthesis, of which 19 studies (n=31 212) were included in the meta-analysis. On meta-analysis, involuntary rather than voluntary hospitalisation of minors was associated with a diagnosis of psychosis (eight studies; odds ratio 3•63, 95% CI 2•43-5•44, p<0•0001), substance misuse (five studies; 1•87, 1•05-3•30, p=0•032), or intellectual disability (four studies; 3•33, 1•33-8•34, p=0•010), as well as presenting with a perceived risk of harm to self (eight studies; 2•05, 1•15-3•64, p=0•015) or to others (five studies; 2•37, 1•39-4•03, p=0•0015). Involuntary hospitalisation was also found to be associated with being aged 12 years or older (three studies; 3•57, 1•46-8•73, p=0•0052) and being from a Black rather than a White ethnic group (three studies; 2•72, 1•88-3•95, p<0•0001). There was substantial between-study heterogeneity for most factors included in the meta-analysis (I² from 51•3% to 92•3%). Narrative synthesis found that more severe illness and poorer global functioning was associated with involuntary hospitalisation.Interpretation Over-representation of involuntary psychiatric hospitalisation in certain groups might begin in childhood, potentially establishing a cycle of inequality that continues into adulthood. Further research into the systemic factors underlying these health-care inequalities and the barriers to accessing less coercive psychiatric treatment is urgently required, with specific consideration of racial and ethnic factors.