Objectives: To examine how outpatient mental health (MH) follow-up after a pediatric MH emergency department (ED) discharge varies by patient characteristics and to evaluate the association between timely follow-up and return encounters. Methods: We conducted a retrospective study of 28 551 children aged 6 to 17 years with MH ED discharges from January 2018 to June 2019, using the IBM Watson MarketScan Medicaid database. Odds of nonemergent outpatient follow-up, adjusted for sociodemographic and clinical characteristics, were estimated using logistic regression. Cox proportional hazard models were used to evaluate the association between timely follow-up and risk of return MH acute care encounters (ED visits and hospitalizations). Results: Following MH ED discharge, 31.2% and 55.8% of children had an outpatient MH visit within 7 and 30 days, respectively. The return rate was 26.5% within 6 months. Compared with children with no past-year outpatient MH visits, those with ≥14 past-year MH visits had 9.53 odds of accessing follow-up care within 30 days (95% confidence interval [CI], 8.75-10.38). Timely follow-up within 30 days was associated with a 26% decreased risk of return within 5 days of the index ED discharge (hazard ratio, 0.74; 95% CI, 0.63-0.91), followed by an increased risk of return thereafter. Conclusions: Connection to outpatient care within 7 and 30 days of a MH ED discharge remains poor, and children without prior MH outpatient care are at highest risk for poor access to care. Interventions to link to outpatient MH care should prioritize follow-up within 5 days of an MH ED discharge.