Maternal depression is identified as a risk factor for childhood psychopathology. This paper investigated whether the time period of initial exposure to maternal depression differs according to its influence on later adolescent emotional disorders. The study analyzed data (n=937) from the National Longitudinal Survey of Children and Youth (NLSCY), a longitudinal study established by Statistics Canada in 1994/5 to investigate child health and development. Adolescent (i.e., gender, chronic health conditions, stressful life events, low household SES) and maternal characteristics (i.e., marital status, chronic health conditions, heavy alcohol use, social support, more than one depressive episode, currently depressed) were analyzed according to whether they significantly influence the likelihood of an adolescent emotional disorder between the ages of 12 to 13 years. Results suggest that there is a sensitive time period of initial exposure to maternal depression. Specifically, children initially exposed to maternal depression between the ages of two and five years old were significantly more likely to experience symptoms of depression and anxiety in adolescence when compared to their unexposed counterparts.