INTRODUCTION: Access to antiretroviral therapy (ART) is a global priority. However, the attrition across the continuum of care for HIV-infected children between their HIV diagnosis and ART initiation is not well known. We analyzed the time from enrollment into HIV care to ART initiation in HIV-infected children within the International Epidemiology Databases to Evaluate AIDS (IeDEA) Global Cohort Consortium. METHODS AND FINDINGS: We included 135,479 HIV-1-infected children, aged 0-19 years and ART-naïve at enrollment, between 1 January 2004 and 31 December 2015, in IeDEA cohorts from Central Africa (3 countries; n = 4,948), East Africa (3 countries; n = 22,827), West Africa (7 countries; n = 7,372), Southern Africa (6 countries; n = 93,799), Asia-Pacific (6 countries; n = 4,045), and Latin America (7 countries; n = 2,488). Follow-up in these cohorts is typically every 3-6 months. We described time to ART initiation and missed opportunities (death or loss to follow-up [LTFU]: last clinical visit >6 months) since baseline (the date of HIV diagnosis or, if unavailable, date of enrollment). Cumulative incidence functions (CIFs) for and determinants of ART initiation were computed, with death and LTFU as competing risks. Among the 135,479 children included, 99,404 (73.4%) initiated ART, 1.9% died, 1.4% were transferred out, and 20.4% were lost to follow-up before ART initiation. The 24-month CIF for ART initiation was 68.2% (95% CI: 67.9%-68.4%); it was lower in sub-Saharan Africa-ranging from 49.8% (95% CI: 48.4%-51.2%) in Central Africa to 72.5% (95% CI: 71.5%-73.5%) in West Africa-compared to Latin America (71.0%, 95% CI: 69.1%-72.7%) and the Asia-Pacific (78.3%, 95% CI: 76.9%-79.6%). Adolescents aged 15-19 years and infants <1 year had the lowest cumulative incidence of ART initiation compared to other ages: 62.2% (95% CI: 61.6%-62.8%) and 66.4% (95% CI: 65.7%-67.0%), respectively. Overall, 49.1% were ART-eligible per local guidelines at baseline, of whom 80.6% initiated ART. The following children had lower cumulative incidence of ART initiation: female children (p < 0.01); those aged <1 year, 2-4 years, 5-9 years, and 15-19 years (versus those aged 10-14 years, p < 0.01); those who became eligible during follow-up (versus eligible at enrollment, p < 0.01); and those receiving care in low-income or lower-middle-income countries (p < 0.01). The main limitations of our study include left truncation and survivor bias, caused by deaths of children prior to enrollment, and use of enrollment date as a proxy for missing data on date of HIV diagnosis, which could have led to underestimation of the time between HIV diagnosis and ART initiation. CONCLUSIONS: In this study, 68% of HIV-infected children initiated ART by 24 months. However, there was a substantial risk of LTFU before ART initiation, which may also represent undocumented mortality. In 2015, many obstacles to ART initiation remained, with substantial inequities. More effective and targeted interventions to improve access are needed to reach the target of treating 90% of HIV-infected children with ART.