Objective: The aim of the study was to determine whether young women with polycystic ovary syndrome (PCOS) have evidence of early structural changes in echocardiographic parameters as a measurement of cardiovascular risk. Methods: We investigated the association of PCOS and echocardiographic parameters in 984 black and white women in the Coronary Artery Risk Development in Young Adults (CARDIA) study, a cohort followed prospectively for 20 yr. Women ages 34-46 (Year 16) completed questionnaires recalling symptoms of oligomenorrhea and hirsutism in their 20s and 30s. Serum androgens were obtained at Year 2. Women in their 20s and 30s were classified into four mutually exclusive groups: 1) PCOS; 2) isolated oligomenorrhea (IO); 3) isolated hyperandrogenism (IH); and 4) reference group. Outcome measures were defined as echocardiography data from Year 5. We used multivariable linear regression models to evaluate the association of PCOS and its components with left ventricular (LV) mass index, left atrial (LA) diameter, LV ejection fraction (LVEF), and mitral inflow early wave to late wave ratio. Results: Among 984 participants, 42 women (4.3%) were classified as PCOS, 67 (6.8%) as IO, and 178 (18.0%) as IH. In multivariable linear regression analyses, women with PCOS had a 3.14 g/m2.7(95% confidence interval, 0.48-5.81) higher LV mass index compared to the reference group (approximately 10% higher). PCOS women also had a 0.11 cm/m (95% confidence interval, 0.02-0.19) larger LA diameter, after adjustment for age and race. Conclusion: PCOS, but not IO or IH, is associated with a higher LV mass index and larger LA diameter in young women, suggestive of early adverse cardiac remodeling. Additional longitudinal studies are needed to evaluate whether this difference persists over time.