Background: There has been little research on the long-term relationship between unemployment experiences and mental health over the life course. This article investigates the relationship between youth unemployment as well as that of unemployment experiences during later periods and mental health at ages 16, 21, 30 and 42 years. Methods: The study makes use of the ‘Northern Swedish Cohort’ (NSC), a 27-year prospective cohort study. The cohort, investigated at ages 16, 18, 21, 30 and 42 years, consisted of all graduates from compulsory school in an industrial town in Sweden. Of the original 1083 participants, 94.3% of those still alive were still participating at the 27-year follow up. Mental health, measured through a three-item index of nervous symptoms, depressive symptoms and sleeping problems, was analysed using a repeated measures linear mixed models approach using ages 16, 21, 30 and 43 years. Unemployment exposure was measured as exposure to at least a 6-month spell during three periods; 18–21, 21–30 and 30–42 years. Results: Youth unemployment was shown to be significantly connected with poorer mental health at all three target ages, 21, 30 and 42 years. Later singular unemployment experiences did not appear to have the same long-term negative effects. There was however an accumulation in poorer mental health among respondents with unemployment experiences during two, and even more so three, of the periods. Conclusion: There are long-term mental health scarring effects of exposure to youth unemployment and multiple exposure to unemployment during the life course.