Obesity is a risk factor for mortality and relapse of certain cancers. However, existing evidence for pediatric leukemia is inconsistent. The aim of this systematic review and meta-analysis was to evaluate the association between obesity at diagnosis and pediatric acute leukemia mortality and relapse. This study systematically searched MEDLINE and EMBASE from inception to February 5, 2015. Random-effect models were used to generate pooled estimates of study-specific hazard ratios (HR) and 95% confidence intervals (CI). Eleven studies were included. An increased risk of mortality with a high BMI at diagnosis was observed (overall survival: HR = 1.30, 95% CI = 1.16–1.46 and event-free survival: HR = 1.46, 95% CI = 1.29–1.64). Only two studies reported HR for relapse; one reported a reduced risk, while the other reported an increased risk. A high BMI at diagnosis is associated with poor overall and event-free survival among pediatric acute leukemia patients. Targeted therapeutic approaches for obese pediatric leukemia patients may potentially improve survival outcomes.