Common mental disorders are increasingly recognized as a serious public health concern globally. This study reports an age-period-cohort (APC) analysis of mental wellbeing to help identify high-risk groups.Data from Scottish Health Survey from 2008 to 2021 for adults aged 16+ was used with mental wellbeing measured with three different tools: the General Health Questionnaire-12 (GHQ-12), the Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) and the Revised Clinical Interview Schedule (CIS-R). A graphical analysis was performed using hexamap and Intrinsic Estimator models were employed to estimate the separate effects for age, period and birth cohorts on mental wellbeing.Age evidenced the most pronounced pattern with a U-shape curve indicative of a deterioration of mental health as individuals enter adulthood, reaching a nadir in their late 50s/ early 60s before gradually improving thereafter. Mental health trends across cohorts were largely stable, although there was a noticeable, albeit non-significant, increase in mental health issues among people born in late 1990s-to mid-2000s. After adjusting for APC effects, better mental health was found for males, people with higher incomes, employed and those currently married. Medium to high level of physical activity were also associated with better mental wellbeing.The study supports arguments for greater attention to mental health among those are working-age adults and for younger generations born after the 1980s. Associations with sex, socio-economic factors may help guide targeting of public health measures while associations with a healthy physical lifestyle support arguments at measures intended to promote a mental health through physical activity.