Importance: Despite great expense and little evidence supporting use over corticosteroids, prescriptions for repository corticotropin (H. P. Acthar Gel; Mallinckrodt Pharmaceuticals) have increased markedly. Aggressive sales tactics and payments from the manufacturer may influence prescribing behavior for this expensive medication. Objective: To characterize industry payments to physician specialists who prescribe corticotropin in the Medicare program. Design, Setting, and Participants: This study was a cross-sectional analysis of Centers for Medicare & Medicaid Services 2015 Part D prescribing data linked to 2015 Open Payments data. Nephrologists, neurologists, and rheumatologists with more than 10 corticotropin prescriptions (frequent prescribers) in 2015 were included. Exposures: Frequency, category, and magnitude of corticotropin-related payments from Mallinckrodt recorded in the Open Payments database. Main Outcomes and Measures: Frequency, category, and magnitude of corticotropin-related payments from Mallinckrodt, as well as corticotropin prescriptions and expenditures for Medicare beneficiaries. Results: Of the 235 included physicians, 65 were nephrologists; 59, neurologists; and 111, rheumatologists. A majority of frequent corticotropin prescribers (207 [88%]) received corticotropin-related payments from Mallinckrodt. The median (range) total payment for 2015 was $189 ($11-$138 321), with the highest payments ranging from $56 549 to $138 321 across the specialties. More than 20% of frequent prescribers received more than $10 000 and the top quartile of recipients received a median (range) of $33 190 ($9934-$138 321) in total payments per prescriber. Payments for compensation for services other than consulting contributed the most to the total amount. Mallinckrodt payments were positively associated with greater Medicare spending on corticotropin (β = 1.079; 95% CI, 1.044-1.115; P < .001), with every $10 000 in payments associated with a 7.9% increase (approximately $53 000) in Medicare spending on corticotropin. There was no association between corticotropin-related payments and spending on prescriptions for synthetic corticosteroids. Conclusions and Relevance: In this study, most nephrologists, neurologists, and rheumatologists who frequently prescribe corticotropin received corticotropin-related payments from Mallinckrodt. These findings suggest that financial conflicts of interest may be driving use of corticotropin in the Medicare program.