This investigation was undertaken to explore and compare the effect of bipolar I disorder (BD) and major depressive disorder (MDD) on workforce function. The data for this analysis were procured from the Canadian Community Health Survey (CCHS 1.2). The sample consisted of 20,747 individuals (>or=18 years or older and currently working); the proportions screening positive for lifetime BD and MDD were 2.4% and 11.2%, respectively. Individuals with BD or MDD had a significantly lower mean annual income, compared to people without these disorders. Individuals with BD had a significantly lower annual income when compared to MDD (p < 0.05). Results from a multiple logistic regression also indicate that employed individuals with BD had greater odds of reporting one or more mental health disability days in the past two weeks, compared with those with MDD (OR = 1.6; 95% CI = 1.0 to 2.6). Currently employed individuals with BD had lower odds of "good job security" relative to those with MDD (OR = 0.6 95% CI = 0.5 to 0.9). The data herein underscore the pernicious effect of BD on workforce function, and suggest that opportunistic screening for BD in all individuals utilizing employment assistance programs for depression might be warranted.