OBJECTIVE: Suicide rates among young people are rising. Health care visits provide opportunities for identification and intervention, yet studies have been limited by small or circumscribed samples. This study sought to expand the knowledge base by examining health care encounters and diagnoses among young people who later died by suicide. METHODS: This case-control study examined diagnoses of mental and general medical disorders and health care utilization in the 30 and 365 days before suicide death in nine large U.S. health care systems. Data (years 2000-2015) from 445 suicide decedents ages 10-24 years were matched with data from 4,450 control group patients. RESULTS: Suicide decedents were more likely to have at least one mental disorder diagnosis (51% vs. 16%; adjusted OR [AOR]=5.74, 95% CI=4.60-7.18) and had higher rates of nearly all mental health conditions. Substance use disorders were common (12%) and more likely (AOR=8.50, 95% CI=5.53-13.06) among suicide decedents. More than one in three (42%) suicide decedents had a health care visit in the month before death, and nearly all (88%) had a visit in the previous year. CONCLUSIONS: Despite the greater likelihood of suicide associated with mental disorder diagnoses, such disorders were present among only 51% of suicide decedents. High rates of health care utilization among suicide decedents indicate a need for improving identification of mental health conditions and suicide risk across the health care system. Increased substance use screening may help identify youths at high risk because substance use disorders were significantly more prevalent and likely among suicide decedents.