In recent years, psychotropic drug use among children and adolescents in Europe and USA has increased. However, the majority of psychotropic drugs are not formally approved for use in children and adolescents, and consequently, use is often off-label. The objectives were to describe time trends in off-label prescribing rates and the most commonly used types of psychotropic drugs by age and gender in Danish children and adolescents. Using the Register of Medicinal Product Statistics, we identified all prescriptions for sedatives, hypnotics and antidepressants filled for children and adolescents in 2006-2012. Information on diagnoses was obtained from the Danish National Registry of Patients and allowed classification of prescriptions as either on- or off-label. We identified 186,831 prescriptions filled for 29,851 children and adolescents: 88.0% of these were classified as off-label. During 2006-2012, off-label rates for sedatives and hypnotics increased significantly, except for prescriptions for girls aged 15-17 years [range 24.1-98.2% (girls), 31.9% to 99.0% (boys)]. In the same period, the number of registered melatonin prescriptions (all off-label) increased expansively. For antidepressants, we found decreasing trends in off-label rates over time [range 94.5-65.6% (girls), 93.8-71.2% (boys)]. Off-label prescribing of psychotropic drugs to Danish children and adolescents is common. Off-label rates for sedatives and hypnotics increased in the period of 2006-2012, whereas off-label rates for antidepressants declined. Off-label rates might be underestimated and should be considered a conservative estimate.