Do young women with polycystic ovary syndrome (PCOS) or endometriosis report more psychological distress than their peers without a history of these conditions?Young women (aged 18-23 years) with PCOS or endometriosis had a greater risk of moderate to severe psychological distress than women without a history of these conditions.Psychological distress appears common among women with PCOS and endometriosis. However, population-based studies that examine the psychological outcomes for adolescents and young women are generally absent from the literature.This is a secondary analysis of data collected from 17 015 young, Australian women participating in a national, longitudinal cohort study. Women were first surveyed in 2012-2013 when they were aged 18-23 years. In 2014, women completed the second survey when they were aged 19-24 years and 11324 (67%) women responded.We analysed data from 11 238 women who participated in both Surveys 1 and 2 and who responded to questions about PCOS and endometriosis. Using logistic regression, we compared the odds of moderate to severe psychological distress at Surveys 1 and 2 for women reporting a recent diagnosis (within the last 12 months) of PCOS or endometriosis and women with a pre-existing diagnosis, with that for women without a history of these conditions.At Survey 2, around 60% of women reporting a diagnosis of PCOS or endometriosis had moderate to severe levels of psychological distress. Compared to women without a history of these conditions, the odds of moderate to severe psychological distress at Survey 2 were significantly higher for women recently diagnosed with PCOS [Adjusted Odds Ratio (AOR) = 1.62, 95% CI = 1.21-2.18] or endometriosis (AOR= 1.77; 95% CI = 1.20-2.63) and for women with a pre-existing diagnosis of PCOS (AOR = 1.57, 95% CI = 1.30-1.89) or endometriosis (AOR = 1.61; 95% CI = 1.26-2.06). Women recently diagnosed with PCOS or endometriosis also had a greater likelihood of moderate to severe distress in the year prior to their diagnosis. The association between PCOS and psychological distress was attenuated when adjusting for BMI, but hormonal contraceptive use did not attenuate the risk of distress among the women with PCOS or endometriosis.All data were self-reported and, therefore, the diagnoses of PCOS or endometriosis were not confirmed by a medical practitioner.Health professionals should be aware of the potential psychosocial and healthcare needs among young women with these conditions, particularly women with PCOS who are obese. While hormonal contraceptives may help to regulate the hormonal aspects of these conditions, they do not appear to reduce women's psychological distress. Because psychological distress among the young women in this study remained elevated even after diagnosis, this supports the need for multidisciplinary health care to help women adjust to their diagnosis and treatment regimens and facilitate positive, long-term mental health outcomes. Future research that examines medical and psychosocial sources of distress for young women with PCOS and endometriosis is needed.I.J.R. was supported by an Australian National Health and Medical Research Council Centre for Research Excellence (grant number: APP1000986). G.D.M. is funded by the Australian Research Council Future Fellowship (FT120100812). The Australian Longitudinal Study on Women's Health is funded by the Australian Government Department of Health. H.T. is supported by an Australian National Health and Medical Research Council Practitioner Fellowship. The authors declare that no competing interests exist.N/A.