Objectives: This multicenter study examines the performance of the Manchester Triage System (MTS) after changing discriminators, and with the addition use of abnormal vital sign in patients presenting to pediatric emergency departments (EDs). Design: International multicenter study Settings: EDs of two hospitals in The Netherlands (2006-2009), one in Portugal (November-December 2010), and one in UK (June-November 2010). Patients: Children (< 16years) triaged with the MTS who presented at the ED. Methods: Changes to discriminators (MTS 1) and the value of including abnormal vital signs (MTS 2) were studied to test if this would decrease the number of incorrect assignment. Admission to hospital using the new MTS was compared with those in the original MTS. Likelihood ratios, diagnostic odds ratios (DORs), and c-statistics were calculated as measures for performance and compared with the original MTS. To calculate likelihood ratios and DORs, the MTS had to be dichotomized in low urgent and high urgent. Results: 60,375 patients were included, of whom 13% were admitted. When MTS 1 was used, admission to hospital increased from 25% to 29% for MTS ` very urgent' patients and remained similar in lower MTS urgency levels. The diagnostic odds ratio improved from 4.8 (95% CI 4.5-5.1) to 6.2 (95% CI 5.9-6.6) and the c-statistic remained 0.74. MTS 2 did not improve the performance of the MTS. Conclusions: MTS 1 performed slightly better than the original MTS. The use of vital signs (MTS 2) did not improve the MTS performance.