BACKGROUND: Chronic headache after traumatic brain injury (TBI) is a common, yet disabling, disorder whose diverse clinical characteristics and treatment needs remain poorly defined. OBJECTIVE: To examine diagnostic coding patterns and cost among military Veterans with comorbid chronic headache and TBI. METHODS: We identified 141,125 post-9/11 era Veterans who served between 2001 and 2019 with a headache disorder diagnosed after TBI. We first identified patterns of Complex Headache Combinations (CHC) and then compared the patterns of healthcare costs in 2022-dollar values in the three years following the TBI diagnosis. RESULTS: Veterans had diverse individual headache and CHC diagnoses with uniformly high cost of care. Post-whiplash and post-TBI CHCs were common and consistently associated with higher costs after TBI than those with other types of headache and CHCs. Post-TBI migraine had the highest unadjusted mean inpatient ($27,698), outpatient ($61,417), and pharmacy ($4,231) costs, which persisted even after adjustment for confounders including demographic, military, and clinical characteristics. CONCLUSION: Headache diagnoses after TBI, particularly those diagnosed with post-traumatic headache, are complex, and associated with dual high cost and care burdens. More research is needed to examine whether this higher expenditure reflects more intensive treatment and better outcomes or refractory headache with worse outcomes.