Abstract Background There is concern that rates of mental disorders may be increasing although findings disagree. Using an innovative design with a daughter-mother data set we assess whether there has been a generational increase in lifetime ever rates of major depressive disorder, generalised anxiety disorder, panic disorder, and post-traumatic stress disorder (PTSD) experienced prior to 30 years of age. Methods Pregnant women were recruited during 1981–1983 and administered the Composite International Diagnostic Interview (CIDI) at the 27-year follow-up (2008–11). Offspring were administered the CIDI at the 30-year follow-up (2010–2014). Comparisons for onset of diagnosis are restricted to daughter and mother dyads up to 30 years of age. To address recall bias, disorders were stratified into more (≥12 months duration) and less persistent episodes (