Objective Telomeres are DNA-protein complexes that protect chromosome ends from DNA damage and are surrogate biomarkers of cellular ageing. Current evidence, almost entirely from cross-sectional observations, supports negative associations between leukocyte telomere length (LTL) and adverse lifestyle factors and cardio-metabolic risk factors. Polycystic ovary syndrome (PCOS), the most common gynecological endocrine disorder, is associated with inflammation and oxidative stress, both factors associated with accelerated telomere attrition. We therefore hypothesized that LTL would be shorter and decrease more rapidly in women with PCOS in comparison to a control population. Design Population-based cohort study: women of Northern Finland Birth Cohort 1966, with clinical examinations at ages 31 and 46. The sample included self-reported PCOS (PCOS) (age 31:N=190; age 46:N=207) and referent women (age 31:N=1054; age 46:N=1324) with data on LTL. Methods The association between LTL and PCOS at ages 31 and 46 was analyzed by linear regression models adjusted for BMI, smoking, alcohol consumption and socioeconomic status at the corresponding age. Results Women with PCOS had similar mean LTL at ages 31 and 46 (P>0.4 for both). The mean LTL change between ages 31 and 46 did not differ between groups (P=0.19). However, we observed a significant LTL attrition between ages 31 and 46 in the reference population (P<0.001), but not in women with PCOS (P=0.96). Conclusions This finding may suggest a difference in LTL attrition rate in women with PCOS, an unexpected finding that might affect their risk of age-related disease. Further research is needed to clarify the underlying mechanisms.