Greater attained height and greater body mass index (BMI; weight (kg)/height (m)(2)) in young adulthood have been associated with glioma risk, but few studies have investigated the association with body size at birth or during childhood, when the brain undergoes rapid cell growth and differentiation. The Copenhagen School Health Records Register includes data on 320,425 Danish schoolchildren born between 1930 and 1989, with height and weight measurements from ages 7-13 years and parentally recorded birth weights. We prospectively evaluated associations between childhood height and BMI, birth weight, and adult glioma risk. During follow-up (1968-2010), 355 men and 253 women aged ≥18 years were diagnosed with glioma. In boys, height at each age between 7 and 13 years was positively associated with glioma risk; hazard ratios per standard-deviation score at ages 7 (approximately 5.1 cm) and 13 (approximately 7.6 cm) years were 1.17 (95% confidence interval (CI): 1.05, 1.30) and 1.21 (95% CI: 1.09, 1.35), respectively. No associations were observed for childhood height in girls or for BMI. Birth weight was positively associated with risk (per 0.5 kg: hazard ratio = 1.13, 95% CI: 1.04, 1.24). These results suggest that exposures associated with higher birth weight and, in boys, greater height during childhood may contribute to the etiology of adult glioma.