The influence of parental and early childhood factors on adolescent obesity was investigated using a longitudinal model of body mass index (BMI) from birth to 14 years. Trajectories of BMI using linear mixed model (LMM) analysis were used to investigate the influence of early parental and childhood factors on BMI at 14 years in the Raine birth cohort study over eight follow-ups ( n = 1403). An inverse relationship between parental education attainment and BMI was found (mothers x2 = 21.75, p = 0.016; LMM p = 0.043; fathers x2 = 21.19, p =0.020; LMM p . 0.05). More overweight adolescents had mothers who smoked during pregnancy ( x2 = 12.60, p = 0.002). Parental birth weight and BMI across years ( p , 0.001) were strongly associated with adolescent obesity (LMM p , 0.05). Obese adolescents visited the park or playground infrequently as toddlers ( p , 0.05). Results for early home environment factors were mixed. Maternal education, parental birth weight, and parental BMI were the strongest influences on their child’s BMI from birth to adolescence.