ImportanceGrowth in financing has underpinned progress in most areas of health. Adolescent health has recently become a global priority, with inclusion in the Global Strategy for Women’s, Children’s and Adolescents’ Health, but little is known about patterns of financing and development assistance for adolescent health (DAAH).ObjectiveTo provide estimates of DAAH at global, regional, and country levels.Design, Setting, and ParticipantsIn this quality improvement study, data from the Creditor Reporting System were used to estimate flows of total DAAH and per-adolescent DAAH and to assess its distribution by donors, regions, and countries and the leading causes of burden of disease (ie, disability-adjusted life-years) in 132 developing countries between January 1, 2003, and December 31, 2015. Through use of a key word search and various funding allocation methods, 2 sets of estimates were produced: adolescent-targeted DAAH that included disbursements to projects with a primary adolescent health target and adolescent-inclusive DAAH that included disbursements to projects with either a primary or partial adolescent health target, as well as projects that could benefit adolescent health but did not include age-related key words.Main Outcomes and MeasuresEstimates of DAAH distinguishing between adolescent-targeted and adolescent-inclusive DAAH.ResultsThere were 19 921 projects in 132 countries in the adolescent-targeted estimation between 2003 and 2015, with a total funding amount of $3634.6 million, accounting for 1.6% of total development assistance for health. The top 5 donors (Global Fund to Fight AIDS, Tuberculosis and Malaria, $806.8 million; United Nations Population Fund, $401.3 million; United States, $389.9 million; United Kingdom, $251.8 million; and International Development Association, $218.6 million) together provided 56.9% of all adolescent-targeted DAAH. Sub-Saharan Africa received the largest cumulative DAAH per adolescent ($5.37) during the period. In 2015, among the 10 leading causes of disability-adjusted life-years, HIV and AIDS received the largest DAAH, followed by interpersonal violence, tuberculosis, and diarrheal diseases. Other leading causes, including road injuries and depressive disorders, received few disbursements, especially among the low-income countries.Conclusions and RelevanceDespite an increasing rate, DAAH composed a small proportion of total development assistance for health, suggesting that adolescent health has gained little donor attention. Moreover, recent allocations of DAAH have not aligned well with either the burden of disease or the areas where the benefits of investment are likely to be high.