For children with acute lymphoblastic leukemia (ALL), the impact of obesity at diagnosis and weight change during induction on survival is uncertain. Objectives of this study were to describe the relationship between obesity and weight change during induction and event-free survival (EFS) and overall survival (OS). Participants were children 2-18 years old with ALL diagnosed between January 2001 and September 2006. Univariate and multiple regression analyses were conducted. In total 238 children were included; 21 (8.8%) were obese at diagnosis. Obese patients, compared with non-obese patients, had lower 5-year EFS (62.2±12.1% vs. 83.6±2.6%; p =0.02) and OS (80.7±8.7% vs. 92.9±1.9%; p =0.005). In univariate analysis, weight gain during induction was associated with better EFS (hazard ratio [HR] =0.89, 95% confidence interval [CI] 0.82-0.97; p =0.009) and OS (HR =0.81, 95% CI 0.74-0.90; p <0.0001). Obese pediatric patients with ALL have inferior survival while increased weight during induction may be associated with better survival. Causes of weight loss during induction should be aggressively managed.