BACKGROUND: Daily or serial evaluation of multiple organ dysfunction syndrome (MODS) scores may provide useful information. We aimed to validate the daily (d) PELOD-2 score using the set of seven days proposed with the previous version of the score. METHODS: In all consecutive patients admitted to nine pediatric intensive care units (PICUs) we prospectively measured the dPELOD-2 score at day 1, 2, 5, 8, 12, 16, and 18. PICU mortality was used as the outcome dependent variable. The discriminant power of the dPELOD-2 scores was estimated using the area under the ROC curve and the calibration using the Hosmer-Lemeshow chi-square test. We used a logistic regression to investigate the relationship between the dPELOD-2 scores and outcome, and between the change in PELOD-2 score from day 1 and outcome. RESULTS: We included 3669 patients (median age 15.5 months, mortality rate 6.1%, median length of PICU stay 3 days). Median dPELOD-2 scores were significantly higher in nonsurvivors than in survivors (p < 0.0001). The dPELOD-2 score was available at least at day 2 in 2057 patients: among the 796 patients without MODS on day 1, 186 (23.3%) acquired the syndrome during their PICU stay (mortality 4.9% vs. 0.3% among the 610 who did not; p < 0.0001). Among the 1261 patients with MODS on day 1, the syndrome worsened in 157 (12.4%) and remained unchanged or improved in 1104 (87.6%) (mortality 22.9% vs. 6.6%; p < 0.0001). The AUC of the dPELOD-2 scores ranged from 0.75 (95% CI: 0.67-0.83) to 0.89 (95% CI: 0.86-0.91). The calibration was good with a chi-square test between 13.5 (p = 0.06) and 0.9 (p = 0.99). The PELOD-2 score on day 1 was a significant prognostic factor; the serial evaluation of the change in the dPELOD-2 score from day1, adjusted for baseline value, demonstrated a significant odds ratio of death for each of the 7 days. CONCLUSIONS: This study suggests that the progression of the severity of organ dysfunctions can be evaluated by measuring the dPELOD-2 score during a set of 7 days in PICU, providing useful information on outcome in critically ill children. Its external validation would be useful.