Objective To develop new patient-reported outcome (PRO) measures to better understand feelings of loss in caregivers of individuals with traumatic brain injury (TBI). Design Cross-sectional survey study. Setting Three TBI Model Systems rehabilitation hospitals, an academic medical center, and a military medical treatment facility. Participants Caregivers (N=560) of civilians with TBI (n=344) or service members/veterans (SMVs) with TBI (n=216). Interventions Not applicable. Main Outcome Measures Traumatic Brain Injury Caregiver Quality of Life (TBI-CareQOL) Feelings of Loss-Self and TBI-CareQOL Feelings of Loss-Person with Traumatic Brain Injury item banks. Results While the initial exploratory and confirmatory factor analyses of the feelings of loss item pool (98 items) potentially supported a unidimensional set of items, further analysis indicated 2 different factors: Feelings of Loss-Self (43 items) and Feelings of Loss-Person with TBI (20 items). For Feelings of Loss-Self, an additional 13 items were deleted due to item-response theory-based item misfit; the remaining 30 items had good overall model fit (comparative fit index [CFI]=0.96, Tucker-Lewis index [TLI]=.96, root mean squared error of approximation [RMSEA]=.10). For Feelings of Loss-Other, 1 additional item was deleted due to an associated high correlated error modification index value; the final 19 items evidenced good overall model fit (CFI=0.97, TLI=.97, RMSEA=.095). The final item banks were developed to be administered as either a Computer Adaptive Test (CAT) or a short-form (SF). Clinical experts approved the content of the 6-item SFs of the 2 measures (3-week test-retest was r =.87 for Feelings of Loss-Self and r =.85 for Feelings of Loss-Person with TBI). Conclusions The findings from this study resulted in the development of 2 new PROs to assess feelings of loss in caregivers of individuals with TBI; TBI-CareQOL Feelings of Loss-Self and TBI-CareQOL Feelings of Loss-Person with TBI. Good psychometric properties were established and an SF was developed for ease of use in clinical situations. Additional research is needed to determine concurrent and predictive validity of these measures in the psychological treatment of those caring for persons with TBI. Highlights • Feelings of loss are common in caregivers of persons with traumatic brain injury. • Two new self-report measures of caregiver feelings of loss were developed. • These self-report measures can help identify feelings of entrapment in caregivers.