ImportanceApproximately 1 in 6 youth in the US have a mental health condition, and suicide is a leading cause of death among this population. Recent national statistics describing acute care hospitalizations for mental health conditions are lacking.ObjectivesTo describe national trends in pediatric mental health hospitalizations between 2009 and 2019, to compare utilization among mental health and non–mental health hospitalizations, and to characterize variation in utilization across hospitals.Design, Setting, and ParticipantsRetrospective analysis of the 2009, 2012, 2016, and 2019 Kids’ Inpatient Database, a nationally representative database of US acute care hospital discharges. Analysis included 4 767 840 weighted hospitalizations among children 3 to 17 years of age.ExposuresHospitalizations with primary mental health diagnoses were identified using the Child and Adolescent Mental Health Disorders Classification System, which classified mental health diagnoses into 30 mutually exclusive disorder types.Main Outcomes and MeasuresMeasures included number and proportion of hospitalizations with a primary mental health diagnosis and with attempted suicide, suicidal ideation, or self-injury; number and proportion of hospital days and interfacility transfers attributable to mental health hospitalizations; mean lengths of stay (days) and transfer rates among mental health and non–mental health hospitalizations; and variation in these measures across hospitals.ResultsOf 201 932 pediatric mental health hospitalizations in 2019, 123 342 (61.1% [95% CI, 60.3%-61.9%]) were in females, 100 038 (49.5% [95% CI, 48.3%-50.7%]) were in adolescents aged 15 to 17 years, and 103 456 (51.3% [95% CI, 48.6%-53.9%]) were covered by Medicaid. Between 2009 and 2019, the number of pediatric mental health hospitalizations increased by 25.8%, and these hospitalizations accounted for a significantly higher proportion of pediatric hospitalizations (11.5% [95% CI, 10.2%-12.8%] vs 19.8% [95% CI, 17.7%-21.9%]), hospital days (22.2% [95% CI, 19.1%-25.3%] vs 28.7% [95% CI, 24.4%-33.0%]), and interfacility transfers (36.9% [95% CI, 33.2%-40.5%] vs 49.3% [95% CI, 45.9%-52.7%]). The percentage of mental health hospitalizations with attempted suicide, suicidal ideation, or self-injury diagnoses increased significantly from 30.7% (95% CI, 28.6%-32.8%) in 2009 to 64.2% (95% CI, 62.3%-66.2%) in 2019. Length of stay and interfacility transfer rates varied significantly across hospitals. Across all years, mental health hospitalizations had significantly longer mean lengths of stay and higher transfer rates compared with non–mental health hospitalizations.Conclusions and RelevanceBetween 2009 and 2019, the number and proportion of pediatric acute care hospitalizations due to mental health diagnoses increased significantly. The majority of mental health hospitalizations in 2019 included a diagnosis of attempted suicide, suicidal ideation, or self-injury, underscoring the increasing importance of this concern.