Introduction: Weight loss in newborns delivered by caesarean section is poorly studied in Peru. Objective: To determine the cut-off point for weight variation in the first 24 hours in term newborns delivered by caesarean section to develop excessive weight loss. Material and methods: An analytical study of diagnostic test was carried out. The sample was composed of 143 healthy babies born by cesarean section in Cusco, Peru. The excessive weight loss (> 10%) was considered as a variable of interest and the percentage variation in weight at 24 hours was considered as a variable of exposure. Cut-off points were established for excessive weight loss due to ROC curves and diagnostic validation. Results: The average birth weight was 3262.7 grams and the percentage change in weight at 24 and 72 hours was 4.9% and 8.6%, respectively. The area under the ROC curve was 64.13% (95 %CI; 54.03-74.22). The cut-off point to develop excessive weight loss at 72 hours was 5.47% (S: 51.28%; E: 69.23%; PPV: 38.46% and NPV: 79.12%). For each percentage point increase in weight change at 24 hours, the risk of having excessive weight loss increased by 33% (OR: 1.33; 95% CI; 1.11-1.62; p = 0.003). Conclusions: The variation in weight by 5.47% at 24 hours can predict excessive weight loss in newborns delivered by caesarean section in Cusco, Peru.