To investigate the relationships between work environmental factors and the risk of major depressive disorder (MDD) over one year and to identify factors associated with the outcomes of individuals with MDD.

We conducted a population-based longitudinal study of employees who were randomly selected in Alberta (n = 4239). MDD was assessed using the World Health Organization's Composite International Diagnostic Interview - Auto 2.1.

The one-year incidence of MDD was 3.6% (95% CI: 2.8%-4.6%) overall. It was 2.9% (95% CI: 1.9% - 4.2%) in men and 4.5% (95% CI: 3.3% - 6.2%) in women. The relationships between work environmental factors and MDD differed by sex. In men, high job strain increased the risk of MDD in those who worked 35-40 hours per week; job insecurity and family-work conflict were predictive of MDD. Women who worked 35-40 hours, who reported job insecurity, high effort-reward imbalance and work-family conflict were at higher risk of MDD. Long working hours, negative thinking and having comorbid social phobia were predictive of MDD. Perceived work-family conflict, severity of major depressive episode and symptom of depressed mood were significantly associated with recurrence of MDD.

Job strain, effort-reward imbalance, job insecurity and work-family conflicts are important risk factors for the onset of MDD, and should be targets of primary prevention. However, these work environmental factors appear to operate differently in men and in women. Clinical and psychosocial factors are important in the prognosis of MDD. The factors associated with persistence and recurrence of MDD may be different.