UNLABELLED: Simple clinical markers have poor sensitivity; specificity and predictive value in both infants and adults when predicting the success of weaning from mechanical ventilation. Recently, multi-parametric indices, such as the CROP (Compliance-Respiratory Rate-Oxygenation-Pressure) and the RSB (Rapid-Shallow-Breathing) have been used in adults and subsequently in children. The aim of this study was to test the value of the pediatric CROP and RSB (CROPp, RSBp) and the accuracy of a simplified pediatric CROP (CROPpS) that does not require an arterial blood gas sample. MATERIALS AND METHODS: This prospective study was conducted in a pediatric ICU which does not admit neonates. All infants were intubated and ventilated at the time of entry. Spontaneous tidal volume and maximal negative inspiratory pressure, that are required to assess and calculate the indices, were measured using a Fleish pneumotachograph and a unidirectional valve. The other parameters were recorded or calculated. A maximum 4 hour-duration trial of spontaneous ventilation was then performed. Weaning failure was defined as the requirement of re-ventilation within 48 hours of extubation. The discriminant power of CROPp and RSBp was determined by calculating the area under the receiver operating characteristic (ROC) curve. The best cut-off value of the CROPpS was determined by chi2 optimisation. RESULTS: 39 children (20 males) were included in the trial. They had a median age of 3.2 years and a median duration of mechanical ventilation of 1.3 days. 89.7% of children were successfully weaned of mechanical ventilation. Sensitivity of CROP, and RSB, was 97% and 94%, specificity was 0% and 0%, positive predictive value was 89% and 89%, and negative predictive value was 0% and 0% respectively; the area under the ROC curve was 0.57 and 0.74. The CROP,S was found to be as accurate as the CROP, index using the same cut-off value. Comparison of the 2 groups (success, failure) revealed a significant difference in duration of ventilation (longer in the failure group). CONCLUSION: Even though they correctly classified 87% and 85% of patients respectively, the CROPp and RSBp are not good predictors of weaning from mechanical ventilation as the area under the ROC curve is less than 0.80. Other indices need to be evaluated.