Fellowship-trained orthopaedic oncologists in the US military provide routine clinical care and also must maintain readiness to provide combat casualty care. However, low oncologic procedure volume may hinder the ability of these surgeons to maintain relevant surgical expertise. Other low-volume specialties within the Military Health System (MHS) have established partnerships with neighboring civilian centers to increase procedure volume, but the need for similar partnerships for orthopaedic oncologists has not been examined. The purpose of this study was to characterize the practice patterns of US military fellowship-trained orthopaedic oncologists. We asked the following questions: (1) What are the diagnoses treated by US military fellowship-trained orthopaedic oncologists? (2) What are the procedures performed by US military fellowship-trained orthopaedic oncologists? We queried the Military Data Repository, a centralized repository for healthcare data for all healthcare beneficiaries (active duty, dependents, and retirees) within the Defense Health Agency using the MHS's Management and Reporting Tool for all international common procedure taxonomy (CPT) codes and ICD-9 and ICD-10 codes associated with National Provider Identifier (NPI) numbers of active duty, military fellowship-trained orthopaedic oncologists. Fellowship-trained orthopaedic oncologists were identified by military specialty leaders. Then, we identified all procedures performed by the orthopaedic oncologist based on NPI numbers for fiscal years 2013 to 2022. We stratified the CPT codes by top orthopaedic procedure categories (such as amputation [performed for oncologic and nononcologic reasons], fracture, arthroplasty, oncologic) based on associated ICD codes. These were then tabulated by the most common diagnoses treated. Thirteen percent (796 of 5996) of the diagnoses were oncologic, of which 45% (357 of 796) were malignant. Forty-four percent (158 of 357) of the malignancies were primary and 56% (199 of 357) were secondary; this translates to an average of 2 patients with primary and 2.5 patients with secondary malignancies treated per surgeon per year. During the study period, nine orthopaedic oncologists performed 5996 orthopaedic procedures, or 74 procedures per surgeon per year. Twenty-one percent (1252 of 5996) of the procedures were oncologic; the remaining procedures included 897 arthroplasties, 502 fracture-related, 275 amputations for a nononcologic indication, 204 infections, 142 arthroscopic, and 2724 other procedures. Although military orthopaedic oncologists possess expert skills that are directly translatable to combat casualty care and operational readiness, within MHS hospitals they treat relatively few patients with oncologic diagnoses, and less than one-half of those involve malignancies. Despite postgraduation procedure volume raining stable over the last decade, it is unknown how many new patient visits for oncologic diagnoses and how many corresponding tumor procedures are necessary to maintain competence or build confidence after musculoskeletal oncology fellowship training. It is important to note that there are no military orthopaedic oncology fellowships, and all active duty orthopaedic oncologists undergo training at civilian institutions. Military-civilian partnerships with high-volume cancer centers may enable military orthopaedic oncologists to work at civilian cancer centers to increase their oncologic volume to ensure sustainment of operationally relevant knowledge, skills, and abilities and improve patient care and outcomes.