Onset of mental health disorder peaks during adolescence making continuity of care during this period of life crucial both to ensure a smooth treatment course and high quality of mental health services for adolescents. We aimed to examine which clinical and sociodemographic features predict transfer from child and adolescent mental health services to adult mental health services and if transfer is associated with prognosis. A Danish register study including all 16–17-year-olds with an outpatient contact in child and adolescent mental health services, who were discharged in the period of 1/1/06–10/05/15. Out of 27,170 Danish adolescents, 16% transferred to adult mental health services. Transfer was predicted by schizophrenia (OR 6.16; 95% CI 5.51–6.90) and personality disorders (OR 2.08; 95% CI 1.84–2.34), while hyperkinetic (OR 0.54; 95% CI 0.49–0.59) and pervasive developmental disorders (OR 0.42; 95% CI 0.31–0.58) decreased likelihood of transfer. Transfer was also substantially predicted by inpatient admission (OR 3.37; 95% CI 3.14–3.61) and psychiatric medication (OR 2.07; 95% CI 1.92–2.23). Transfer was associated with higher rates of inpatient admission to adult mental health services (IRR 5.83; 95% CI 4.37–7.77), more psychiatric emergency contacts (IRR 12.0; 95% CI 10.7–13.4), more convictions (IRR 1.40; 95% CI 1.23–1.59) and suicide attempts (IRR 5.70; 95% CI 4.72–6.90). Policy-makers and clinicians should push for improvements and open a discussion of how to ensure continuity of care for adolescents with psychiatric disorders