The BITSS scale (Brussels Infant and Toddler Stool Scale) is an instrument used in the diagnosis and follow-up of infants and young children with infectious diarrhea. It consists of 7 pictures of diapers with different types of stools. Objective: To determine intra and interobserver reliability of the BITSS scale in infants and children using diapers. Patients and Method: Reliability study. Three pediatri-cians with experience in treating childhood infectious diarrhea were selected and, after training in applying the BITSS scale, they evaluated 70 pictures of stools obtained from pediatric patients, representing the 7 different types of stools categorized by the scale (10 images for each item). Two pediatri-cians participated in the interobserver reliability study and performed a blind evaluation of the same pictures, assigning a value to each one, and the third pediatrician participated in the intra-observer analysis, evaluating 70 images on two different occasions, 15 days apart. Interobserver agreement and kappa statistics were determined for the scale and each scale item. Results: 280 measurements were made, 140 for the inter-observer reliability study and 140 for the intra-observer one. The degree of inter-observer agreement for the scale was 85.7%; with a kappa of 0.817 (95% CI 0.72; 0.92), and standard error of 0.05; and the intra-observer kappa for the scale was 0.883 (95% CI 0.80; 0.96), with a standard error of 0.04. Conclusions: The BITSS scale has good intra-and interobserver reliability.