The practice of child marriage has been well-studied among girls, but there has been little information to date about child marriage among boys. This paper presents an analysis of all nationally representative and internationally comparable data on the prevalence of child marriage among boys. Such data are available for 82 countries within the past 10 years, representing 51% of the global population of men. In the countries with data, on average, 4.5 per cent of young men aged 20–24 years were first married or in union before age 18, with a range of values from less than 1 per cent to nearly 30 per cent. Data from all regions show that the practice has become less common compared to 25 years ago. The countries with the highest prevalence of child marriage among boys are geographically diverse and differ from the countries where the practice is most common among girls. Further research is needed on the drivers of the practice and its effects on child grooms.