Smokeless tobacco use is popular in some regions worldwide, but it receives less attention compared to cigarette smoking. We aimed to estimate the recent prevalence of, and trends in, smokeless tobacco use and to examine its associated factors among adolescents aged 12-16 years in 138 countries/territories (hereafter "countries") from 1999 to 2019.Data from the Global Youth Tobacco Survey conducted in 138 countries in 2010-2019 and the National Youth Tobacco Survey conducted in the United States in 2019 were used to calculate the prevalence of current smokeless tobacco use and investigate its associated factors among adolescents aged 12-16 years. We also assessed the trend in the prevalence of smokeless tobacco use in 100 countries that had conducted more than one survey from 1999 to 2019.The overall prevalence of current smokeless tobacco use was 4.4% (95% confidence interval [CI] 4.0-4.9), with 5.7% (5.1-6.3) for boys, 3.1% (2.6-3.5) for girls, 3.9% (3.5-4.4) for adolescents aged 12-14 years and 5.4% (4.8-5.9) for those aged 15-16 years. The prevalence was highest in the South-East Asian region (6.1%, 4.4-7.7) and lowest in the Western Pacific region (2.0%, 1.7-2.4). The prevalence of smokeless tobacco use decreased in 57 of 100 countries, increased in 32 countries, and remained unchanged in 11 countries. Current cigarette smoking (odds ratio [OR]=2.00, 95% CI=1.68-2.39), other tobacco product use (OR=6.03, 95% CI=4.92-7.40), tobacco advertisement exposure (OR=1.44, 95% CI=1.19-1.74), being offered free tobacco products (OR=2.01, 95% CI=1.66-2.42), and not being taught about dangers of smoking (OR=1.28, 95% CI=1.09-1.50) were all positively associated with current smokeless tobacco use.Smokeless tobacco use among adolescents remains a public health concern worldwide. Although the prevalence among adolescents decreased in most countries, it remains high especially in the South-East Asian region. More strict and effective strategies and measures are needed to further curb the smokeless tobacco use among adolescents.