BackgroundStudies using self-reports indicate that individuals with ADHD are at increased risk for functional impairments in social and occupational settings, but evidence around real-life instability remains limited. It is furthermore unclear if these functional impairments in ADHD differ across sex and across the adult lifespan.MethodA longitudinal observational cohort design of 3,448,440 individuals was used to study the associations between ADHD and residential moves, relational instability and job shifting using data from Swedish national registers. Data were stratified on sex and age (18–29 years, 30–39 years, and 40–52 years at start of follow up).Results31,081 individuals (17,088 males; 13,993 females) in the total cohort had an ADHD-diagnosis. Individuals with ADHD had an increased incidence rate ratio (IRR) of residential moves (IRR 2.35 [95% CI, 2.32–2.37]), relational instability (IRR = 1.07 [95% CI, 1.06–1.08]) and job shifting (IRR = 1.03 [95% CI, 1.02–1.04]). These associations tended to increase with increasing age. The strongest associations were found in the oldest group (40–52 years at start of follow). Women with ADHD in all three age groups had a higher rate of relational instability compared to men with ADHD.ConclusionBoth men and women with a diagnosis of ADHD present with an increased risk of real-life instability in different domains and this behavioral pattern was not limited to young adulthood but also existed well into older adulthood. It is therefore important to have a lifespan perspective on ADHD for individuals, relatives, and the health care sector.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12888-023-04713-z.