Background: survivors of childhood acute leukemia are at risk for obesity. The purpose was to evaluate the different clinical measurements of body composition and to compare with body mass index (BMI). Methods: cross-sectional study of 39 survivors with more than ten years of survivorship since diagnosis. Anthropometry and body composition accuracy measurements were determined and also obesity risk factors. Results: obesity prevalence by body fat percentage were: 38.5% for BMI; 46.1% for waist circumference; 51.3% for skinfolds and 56.4% for bioelectrical impedance analysis (BIA). There was a good correlation among the measurements, but BMI underestimated the percent body fat among childhood leukemia survivors in comparison with: waist circumference (-1.03 ± 2.01), skinfolds (-2.95 ± 5.78) and BIA (-3.78 ± 7.4), and this bias appears to be more variable with increasing percent of body fat > 30%. Three patients showed sarcopenia and only one sarcopenic obesity. Waist circumference fat mass was the better predictor of cardiovascular risk factors (LDL-cholesterol: r = 0.703; HDL-cholesterol: r = -0.612; p < 0.05 and hypertension: OR 4.17; IC 95%: 1.012-19.3). Obesity risk factors were: female sex, high-risk tumor, radiotherapy and stem cell transplantation. Conclusions: BMI underestimates obese childhood leukemia survivors in comparison with waist circumference, skinfolds and bioelectrial impedance analysis. BMI use could misclassify obese survivors as non-obese. Female sex, high tumoral risk and coadyuvant treatments (radiotherapy and stem cell transplant) are risk factors for adiposity.