OBJECTIVE. This study assessed the initial psychometric properties of a novel in-home, performance-based instrument for older adults called the In-Home Medication Management Performance Evaluation (HOME-Rx). METHOD. Content validity of the HOME-Rx was determined through the multistep content validity index (CVI) process. Content experts provided qualitative and quantitative judgment of the instrument's ability to measure medication management. The assessment's target population provided qualitative feedback. CVI outcomes informed instrument revisions. RESULTS. Content experts (n = 7) were in agreement that the overall instrument was valid for measuring medication management (scale-level CVI = .95). Six items were deleted because of low agreement (item-level CVI <.80). Twenty-nine minor edits were made to the order of questions and language. Older adult participants (n = 5) reported the instrument was relevant, acceptable, and easy to understand. CONCLUSION. The HOME-Rx appears to be a relevant and valid method to assess performance barriers to medication management in the home.