The current study examines the Theory of Planned Behaviour's (TPB) ability to predict marijuana use among young women who experienced a premarital pregnancy before the age of 18 years, using longitudinal data. The validity of the TPB assumption that all other variables work through TPB constructs is also tested. Indicators of four constructs that have been shown in the literature to be predictive of marijuana use-persistent environmental adversity, emotional distress, adolescent marijuana use and drug use in the social network-were tested as predictors of attitudes, norms and self-efficacy, in a structural equation modelling framework. All paths from distal predictors were through the mediating TPB constructs, in accordance with the tenets of the model. Implications of these findings for the TPB model and for understanding factors that lead to marijuana use are discussed.