Objective: Australian youth mental health services have received significant funding over the past 15 years. We analysed data on hospitalisation due to intentional self-harm to determine whether increased youth services were associated with reduction in a key indicator of youth population mental health. Method: Trends in national self-harm hospitalisation data from 2008 to 2019 for youth (<25 years) and adults (>25 years) were analysed using joinpoint regression. Results: Rates of hospitalisation due to intentional self-harm increased significantly in both male (1.1% per annum, 95% CI [0.2%, 1.9%]) and female (3.0% per annum, 95% CI [0.9%, 5.1%]) youth aged <25 years between 2008 and 2019. Female youth had higher rates of hospitalisation than males, and there were average annual increases of 9.1% (95% CI [2.4%, 16.3%]) and 4.0% (95% CI [0.1%, 7.9%]), and absolute increases of 120% and 47.9%, in the rate of hospitalisation of females aged 0–14 and 15–19, respectively. In contrast, there was no overall change in adults (>25 years). Conclusions: Rates of hospitalisation due to intentional self-harm in Australian youth have increased despite significant investment in youth mental health services. This result could be attributable to several sociocultural factors and suggests a critical need for more hospital-based emergency youth mental health services.