Introduction: the prevalence of undernutrition in the pediatric cancer population can vary considerably, an element that significantly influences the clinical outcome of patients. However, this is a potentially modifiable prognostic factor, which requires timely identification of nutritional risk to guide the nutritional care process. Objectives: to evaluate the operational performance of the Spanish version of the nutritional screening tool for childhood cancer (SCAN) in the context of the validation process of this instrument in a high-complexity hospital in the city of Bogotá, Colombia. Methods: the methodological design for the validation of a diagnostic scale was followed. The final sample consisted of 96 patients between 0 and 17 years with cancer and hospitalized at the Children’s Cancer Center of the HOMI Foundation in Bogota. The SCAN-SP was applied to each patient and a complete nutritional assessment (CNA) was performed as a gold standard to determine nutritional status. Results: 82.3 % (n = 79) of patients were classified “at risk of malnutrition” by SCAN-SP and 69.8 % (n = 67) of the total sample had undernutrition. The evaluation of the operative performance of SCAN-SP against CNA showed excellent results: sensitivity of 100 %, specificity of 59 %, PPV of 85 %, NPV of 100 %, positive likelihood ratio of 2.4, and negative likelihood ratio of 0. Conclusion: the SCAN-SP scale performs well as a nutritional screening tool in pediatric cancer patients, so its use in clinical practice is recommended.