BACKGROUND: Adiposity rebound (AR), the second BMI rise in childhood at around the age of 6 years, is associated with obesity and metabolic alteration in later life. Given that polycystic ovary syndrome (PCOS) has a strong metabolic component, early life growth patterns could reveal a risk of PCOS. Thus, we aimed to investigate the associations between age at AR and PCOS diagnosis and BMI later in life. MATERIALS AND METHODS: This study is part of a prospective, population-based longitudinal study, where women with PCOS diagnosis by age 46 (n = 280) were compared with asymptomatic women (CTRLs, n = 1573). Weight and height data from birth to age 13 years, at age at menarche, and at ages 31 and 46 years were analyzed RESULTS: Women with PCOS had lower birth weight (3357 ± 477 vs. 3 445 ± 505 g, p < 0.001), earlier age at AR (5.2 ± 1.0 vs. 5.6 ± 0.90 years, p < 0.001) and higher BMI from AR onwards compared with controls. Early timing of AR was associated with PCOS diagnosis independently of BMI (OR 1.62, 95% Cl 1.37-1.92). Women with PCOS and early AR had higher BMI at 31 and 46 years when compared to controls with early AR. The age at AR did not associate with T levels at ages 31 or 46 years. CONCLUSIONS: Early AR was associated with PCOS diagnosis and high BMI in adulthood. Adolescent girls with early AR and persisting obesity should be screened for PCOS symptoms, such as persistent irregular cycles and hirsutism.