BACKGROUND Dermatomyositis and polymyositis (DM/PM) are rare, incurable inflammatory diseases that cause progressive muscle weakness and can be associated with increased medical resource use (MRU). When corticosteroid treatment is unsuccessful, patients may receive intravenous immunoglobulin (IVIg), rituximab, or repository corticotropin injection (RCI). This study compared real-world, non-medication MRU between patients treated with RCI and those treated with IVIg and/or rituximab for DM/PM. METHODS Claims of DM/PM patients were analyzed from the combination of three commercial health insurance databases in the United States from July 2009 to June 2014. Patients treated with RCI were propensity score matched to those treated with IVIg, rituximab, and both (IVIg+rituximab) based on demographics, prior clinical characteristics, and prior MRU. Per-patient per-month (PPPM) MRU and costs were compared using Poisson regression and generalized linear modeling, respectively. RESULTS One-hundred thirty-two RCI, 1,150 IVIg, and 562 rituximab patients had an average age of 52.6, 46.6, and 51.7 years, respectively, and roughly two-thirds were female. After matching, there were no significant differences in demographics or prior clinical characteristics. RCI patients had fewer PPPM hospitalizations (0.09 vs 0.17; P=0.049), shorter length of stay (LOS; 3.24 days vs 4.55 days; P=0.004), PPPM hospital outpatient department (HOPD) visits (0.60 vs 1.39; P<0.001), and PPPM physician office visits (2.01 vs 2.33; P=0.035) than IVIg. RCI had fewer PPPM HOPD visits (0.56 vs 0.92; P<0.001) than rituximab. Patients treated with RCI had shorter LOS (2.18 days vs 5.15; P<0.001) and less PPPM HOPD visits (0.53 vs 1.26; P<0.001) than IVIg+rituximab. Total non-medication PPPM costs were 23%-75% lower for RCI compared to IVIg ($2,126 vs $3,964; P<0.001), rituximab ($2,008 vs $2,607; P=0.018), and IVIg+rituximab ($1,234 vs $4,858; P<0.001). CONCLUSION Patients treated with RCI had less PPPM non-medication MRU and costs than those treated with IVIg and/or rituximab, particularly in the hospital setting where significant costs are incurred.