Many autistic youth have complex healthcare needs, resulting in high rates of health service utilization. However, many characteristics of this health service utilization remain unknown. Using whole-of-population data, this study aimed to quantify and compare rates of psychiatric and non-psychiatric health service utilization among autistic and non-autistic youth, with and without co-occurring intellectual disability. A national retrospective cohort study was employed using linked individual-level administrative data for Aotearoa New Zealand youth (aged 0-24 years). Health service utilization outcomes included 11 psychiatric and non-psychiatric domains. Propensity score matching on a range of sociodemographic measures compared groups across health service utilization outcomes. Data were obtained for 19,479 autistic youth, 29% of whom had a co-occurring intellectual disability and 1,561,278 non-autistic youth. Results demonstrated higher rates of mental health service utilization among autistic compared with non-autistic youth, including inpatient (prevalence ratio 5.85; 95% confidence interval 4.93-6.94) and outpatient (prevalence ratio 4.96; 95% confidence interval 4.75-5.18) service use and psychotropic medication dispensing (prevalence ratio 6.83; 95% confidence interval 6.65-7.02), particularly among autistic youth without intellectual disability. Rates of non-psychiatric hospital admissions (prevalence ratio 1.93; 95% confidence interval 1.85-2.01), potentially avoidable hospitalizations (prevalence ratio 1.91; 95% confidence interval 1.82-2.00) and outpatient visits (prevalence ratio 1.99; 95% confidence interval 1.95-2.01) were also higher among autistic youth. Research implications for delivery of healthcare services are discussed.