BACKGROUND: Consumer participation in planning and implementing health care is actively encouraged as a means of improving patient outcomes. In assessing the ability of patients to self-medicate, health professionals can identify areas in which patients need assistance, education, and intervention to optimize their health outcomes after discharge. OBJECTIVE: To develop and validate a tool to quantify the ability of patients to administer their regularly scheduled medications while they are hospitalized. METHODS: Past research enabled us to develop the Self-Administration of Medication (SAM) tool. Using a Delphi technique of 3 rounds, a panel of expert health professionals established the content validity of the tool. For determining level of agreement in using the SAM tool, 56 patients were selected; for each patient, 2 randomly selected nurses completed an assessment. Construct validity and internal consistency were examined by testing the tool in 50 patients and comparing with other validated scales. RESULTS: The 29-item SAM tool had high content validity scores for clarity, representation, and comprehensiveness, with content validity index values ranging from 0.95-1.0. In testing the level of agreement between 2 nurses, out of 43 valid cases, 95.3% of nurses overwhelmingly agreed about the patients' competence to self-administer their drugs. The intraclass correlation coefficient was 0.819 (95% CI 0.666 to 0.902). Internal consistency for the SAM tool was high, with a Cronbach's alpha of 0.899. A moderate to strong correlation was obtained when comparing the SAM tool with other validated measures. CONCLUSIONS: The SAM tool is valid and reliable for quantifying patients' ability to manage their regularly scheduled medications in the hospital setting.