This national cross-sectional study investigates the prevalence rates, regional differences and factors associated with the involuntary inpatient treatment of adolescents in Finland on a chosen day in 2000. The proportion of inpatients with involuntary legal status was 29.5% (n=82) giving a prevalence rate of 2.5 per 10,000/12-17 years old inhabitants. Forty-eight per cent of involuntarily inpatients were 16-17 years old and 62% had psychotic disorders. Twenty-six per cent of inpatients with involuntary legal status were voluntarily admitted. Regional differences of involuntary treatment were rather modest. Psychotic disorders, suicidal acts, and substance use disorders were independently associated with involuntary legal status. There is a need for further studies to investigate the long-term effects of involuntary treatment on the adolescents' subsequent well-being. Further studies on alternatives methods for involuntary treatment are warranted, likewise the clinical guidelines for involuntary treatment practices.