Background. Prevalence of obesity in pediatric patients with rheumatic disease (RD) receiving steroids can be as high as 43%. The aim of this study was to determine the association between low-dose of prednisone and weight gain among children with RD. Methods. We carried out a prospective cohort study. One cohort was comprised of patients exposed to steroids (group B) and the other group was comprised of patients not exposed to steroids (group A). After standardization, all patients were followed for 24 weeks and weight, height, waist circumference, arm circumference and body fat percentage were assessed. Results. There were 20 patients in group A and 32 in group B. In the first group, juvenile rheumatoid arthritis was the main diagnosis (40%) and systemic lupus erythematosus (56%) in the second one. Between groups, from the beginning and during the entire study period there was no difference in the averages of each anthropometric variable, but there were four (12.5%) new cases of obesity in group B and none in group A. Eleven (55%) patients in group A and 18 (56%) of group B showed an increase in the percentage of fat; of these, only in group B patients was there was a statistically significant gain (p <0.01) in all the anthropometric variables studied. Conclusions: Among pediatric patients with RD, receiving low-doses of prednisone seems to be a factor in weight increase.