Background/Aims: It has been reported that children treated for acute lymphoblastic leukemia (ALL) in developed countries show an increased risk of overweight and obesity in adolescence and adulthood. However, the majority of patients who came to our observation in Brazil have low or normal body weight and only one of them was obese. Therefore, we have decided to assess some biochemical parameters possibly related to the intermediate metabolism and body composition in these patients. Methods: Two groups of subjects were studied: 27 survivors of childhood ALL (14.0 ± 4.2 years old; post-treatment interval 8.6 ± 3.9 years) (ALL group) and 17 healthy subjects (12.8 ± 4 years old) (control group) selected on the basis of their kinship with the patients. Results: 14/27 patients of the ALL group and 4/17 of the control group had leptin levels higher than the normal range for age and sex (p < 0.05). The leptin level was significantly higher in the ALL group (15.5 ± 1.8 ng/ml) than in the control group (10.7 ± 2 ng/ml) (p < 0.05). When adjusted by sex, BMI z-score, and age, the level of leptin in patients of the ALL group was 8.5 higher than in subjects of the control group (p = 0.006). Leptin/insulin correlation in the ALL group was 0.08 and in the control group it was +0.585 (p < 0.05). Conclusion: The data indicate the presence of alterations in the homeostatic regulatory mechanisms controlling body weight in Brazilian patients treated for ALL in childhood, still, it did not lead to obesity in the absence of favorable environmental conditions.