The Interagency Integrated Triage Tool (IITT) is a three-tier triage system designed for resource-limited emergency care (EC) settings. This study sought to assess the validity and reliability of a pilot version of the tool in an urban emergency department (ED) in Papua New Guinea.A pragmatic observational study was conducted at Gerehu General Hospital in Port Moresby, commencing eight weeks after IITT implementation. All ED patients presenting within the subsequent two-month period were included. Triage assessments were performed by a variety of ED clinicians, including community health workers, nurses and doctors. The primary outcome was sensitivity for the detection of time-critical illness, defined by ten pre-specified diagnoses. The association between triage category and ED outcomes was examined using Cramer's V correlation coefficient. Reliability was assessed by inter-rater agreement between a local and an experienced, external triage officer.Among 4512 presentations during the study period, 58 (1.3%) were classified as category one (emergency), 967 (21.6%) as category two (priority) and 3478 (77.1%) as category three (non-urgent). The tool's sensitivity for detecting the pre-specified set of time-sensitive conditions was 70.8% (95%CI 58.2-81.4%), with negative predictive values of 97.3% (95%CI 96.7 - 97.8%) for admission/transfer and 99.9% (95%CI 99.7 - 100.0%) for death. The admission/transfer rate was 44.8% (26/58) among emergency patients, 22.9% (223/976) among priority patients and 2.7% (94/3478) among non-urgent patients (Cramer's V=0.351, p=0.00). Four of 58 (6.9%) emergency patients, 19/976 (2.0%) priority patients and 3/3478 (0.1%) non-urgent patients died in the ED (Cramer's V=0.14, p=0.00). The under-triage rate was 2.7% (94/3477) and the over-triage rate 48.2% (28/58), both within pre-specified limits of acceptability. On average, it took staff 3 minutes 34 seconds (SD 1:06) to determine and document a triage category. Among 70 observed assessments, weighted κ was 0.84 (excellent agreement).The pilot version of the IITT demonstrated acceptable performance characteristics, and validation in other EC settings is warranted.This project was funded through a Friendship Grant from the Australian Government Department of Foreign Affairs and Trade and an International Development Fund Grant from the Australasian College for Emergency Medicine Foundation.