There have been conflicting reports regarding the applicability of Trauma Injury Severity Score (TRISS) methodology to evaluate trauma care in a developing country setting. The objective of this study was to apply TRISS methodology to evaluate trauma care in the public hospitals of a Caribbean developing country. A prospective, observational study was conducted in the three major general hospitals in Trinidad. Major trauma patients were included. Demographic data, waiting time in the Emergency Department, and nature of injury (blunt or penetrating) were noted. Revised Trauma Score, Injury Severity Score, and Glasgow Coma Scale were applied to all patients on admission. Hospital outcomes were noted. Predicted outcomes were calculated for adult patients using TRISS methodology. M, Z statistics and receiver operating characteristic (ROC) curve analysis were done. There were 326 trauma patients studied, of whom 279 adults were evaluated by the TRISS methodology. Men were more frequently involved in trauma than women; there was more blunt trauma than penetrating trauma. The M statistic was 0.98 and the overall Z statistic was 5.81. The ROC curve analysis showed TRISS to be a fair discriminator in the study case-mix with an area under the curve of 0.82 (95% confidence interval 0.69-0.96). There is a considerable disparity between predicted and observed outcomes when trauma patients are evaluated by the TRISS methodology in a developing country setting.