Background: Psychological distress is frequently used as an indicator of the mental health of a population. Overall, the mean level of distress is higher in women than in men and tends to decrease in both genders during adulthood. This pattern is primarily attributable to the differential exposure of women and men to specific risk factors over their lifetimes. However, the age distribution for distress may be confounded by a cohort effect. This study aimed to compare the age and birth cohort distribution of psychological distress by gender. Methods: This study was based on data from the National Population Health Survey, a longitudinal population survey conducted in Canada from 1994-1995 to 2010-2011. Growth curve analyses were performed separately in women (n = 9062) and in men (n = 7877) to examine the distribution of psychological distress by age group and birth cohort in Canadians aged 18 years and older.Results: The mean level of psychological distress is higher in women than in men in all age groups and all birth cohorts, and in the 18-29 age group than in older adults. Minor gender differences are found in the distribution of distress when age and birth cohort are examined jointly. In women, the mean level of distress decreases steadily beginning at age 18, reaches its lowest point in the 60-69 age group and rises thereafter without ever reaching the level observed in young adults. In men, it remains stable in the twenties and then follows a pattern similar to that observed in women. This age pattern is more apparent in more recent than in earlier cohorts and is related to variations in employment status, marital status and education during adulthood.Conclusions: Young adults and, to a lesser degree, seniors are at higher risk for psychological distress than other adults. To better understand the epidemiology of psychological distress, future research should focus on the risk factors that are more prevalent in these age groups. A starting point would be to evaluate how employment status, marital status and educational level change during adulthood and have changed over time in women and in men.