Objective: To describe the associations of childhood and adulthood adiposity measures with knee cartilage thickness, volume and bone area in young adults. Methods: Childhood and adulthood adiposity measures (weight, height, waist circumference and hip circumference) of 186 participants were collected in 1985 (aged 7–15 years) and during 2004–2006 (aged 26–36 years). Knee magnetic resonance imaging was conducted during 2008–2010 (aged 31–41 years) and cartilage thickness, volume and bone area were measured using a quantitative approach (Chondrometrics, Germany). Linear regressions were used to examine the above associations. Results: The prevalence of overweight was 7.6% in childhood and 42.1% in adulthood. Childhood weight (β = − 5.57 mm2/kg) and body mass index (BMI) (β = − 11.55 mm2/kg/m2) were negatively associated with adult patellar bone area, whereas adult weight was positively associated with bone area in medial femorotibial compartment (MFTC) (β = 3.37 mm2/kg) and lateral femorotibial compartment (LFTC) (β = 2.08 mm2/kg). Adult waist–hip ratio (WHR) was negatively associated with cartilage thickness (MFTC: β = − 0.011; LFTC: β = − 0.012 mm/0.01 unit), volume (Patella: β = − 20.97; LFTC: β = − 21.71 mm3/0.01 unit) and bone area (Patella: β = − 4.39 mm2/0.01 unit). The change in WHR z-scores from childhood to adulthood was negatively associated with cartilage thickness (MFTC: β = − 0.056 mm), volume (patella: − 89.95; LFTC: − 93.98 mm3), and bone area (patella: − 20.74 mm2). All p-values < 0.05. Conclusions: Childhood weight and BMI were negatively but adult weight was positively associated with adult bone area. Adult WHR and the change in WHR from childhood to adulthood were negatively associated with cartilage thickness, volume, and bone area. These suggest early-life adiposity measures may affect knee structures in young adults.