Unhealthy behaviors including smoking, drinking, and drug use often begin during adolescence and are closely related to morbidity and mortality. This study examines the prevalence and factors associated with substance use among adolescent boys in Bihar, India. Data from the Understanding the Lives of Adolescents and Young Adults (UDAYA), conducted in 2015–16 in two Indian states, was used for analysis (n = 2004 adolescent boys aged 14–19 years). A multivariate logistic regression model was applied to estimate the effect of various correlates on substance use. Prevalence of tobacco consumption (19%) is high, followed by consumption of alcohol (8%) and drug use (1.2%) among adolescent boys in Bihar. One-fifth have ever used at least one substance. Age, education, current schooling status, wealth quintile, household head's educational attainment, and mother's education level are found to be important factors influencing substance use. It is essential to adopt more pointed programs which can effectively reduce substance use among adolescents in this and similar states. Programs related to prevention of substances should be expanded effectively through health education programs, media messages at the grassroots level, especially in the socio-economically backward states in India. [ABSTRACT FROM AUTHOR]