Two hypotheses regarding the effects of pubertal timing on substance use were tested in a prospective study of 221 young adolescents. A maturational-deviance hypothesis predicted that early-maturing girls and late-maturing boys would experience heightened emotional distress, which in turn would influence initiation and use of substances. Alternatively, an early-maturation hypothesis predicted that early-maturing girls would engage in more substance use than all other groups, independent of emotional distress. Early-maturing adolescents reported more substance use within 1 year. Adolescents experiencing elevated levels of negative affect also reported greater substance use within the next year. However, pubertal timing was not related to emotional distress. Results support the early-maturation hypothesis for girls and suggest its extension to boys.