Objective: to identify the Influence of different factors on energy intake and basal metabolic rate in children with cancer at diagnosis. Methods: the basal metabolic rate and energy intake were measured during hospitalization and before treatment. The basal metabolic rate and energy from foods were measured by indirect calorimetry. Data were compared by Student t test and a multiple linear regression. Results: energy intake ranged from 636 to 3063 kcal/d, mean 1956 +/- 530 kcal/d. Measured basal metabolic rate was within 10 % of predict for Schofield equation in ten of fourteen patients. Four patients were classified as hypometabolic. Energy intake was related to kind of tumor (solid tumor), sex (males) and loss weight, while basal metabolic rate was related to the age and sex, but only the age reached statistical significance (p < 0.01). Conclusions: the most influent variables on basal metabolic rate and energy intake were the variables related with age, sex and nutritional status at diagnosis. Physician should be consider the energy requirements of children in order to establish an appropriate nutritional and oncology therapy, and consequently, modify the risk of nutritional deterioration in order to improve the prognostic of patients.