To assess the completeness of the collection of patient-important outcomes and the mismatch between outcomes measured in research and patients' important issues after trauma. Summary Background Data: To date, severe trauma has mainly been assessed using in-hospital mortality. Yet, with 80 to 90% survivors discharged from hospital, it is critical to assess the collection of patient important long-term outcomes of trauma. Methods: Mixed methods study combining a systematic review of outcomes and their comparison with domains elicited by patients during a qualitative study. We searched Medline, EMBASE and clinicaltrials.gov from January 1, 2014 to September 30, 2019 and extracted all outcomes from reports including severe trauma. We compared these outcomes with 97 domains that matter to trauma survivors identified in a previous qualitative study. We defined as patient-important outcome as the 10 most frequently elicited domains in the qualitative study. We assessed the number of domains captured in each report to illustrate the completeness of the collection of patient-important outcomes. We also assessed the mismatch between outcomes collected and what matters to patients. Findings: Among the 116 reports included in the systematic review, we identified 403 outcomes collected with 154 unique measurements tools. Beside mortality, measurement tools most frequently used were the Glasgow Outcome Scale (31.0%, n=36), questions on patients' return to work (20,7%, n=24) and the EQ-5D (19.0%, n=22). The comparison between the outcomes identified in the systematic review and the domains from the qualitative study found that 10.3% (n=12) reports did not collect any patient-important domains and one collected all 10 patient-important domains. By examining each of the 10 patient-important domains, none was collected in more than 72% of reports and only five were among the ten most frequently measured domains in studies. Conclusion: The completeness of the collection of the long-term patient-important outcomes after trauma can be improved. There was a mismatch between the domains used in the literature and those considered important by patients during a qualitative study.