Purpose: This study identified how unlicensed staff members decide to administer medications prescribed pro re nata (PRN) to residents of assisted living (AL) settings designated for persons with dementia. Theories of knowledge, including explicit and implicit knowledge, discretion, and judgment, guided the analysis. Design and Methods: Data were collected and analyzed using qualitative methods. The staff members responsible for medication administration were shadowed for 6 consecutive days in three Oregon ALs. In-person interviews were conducted with 16 staff members, and residents' medication records were reviewed. Results: Medication aides' decisions to administer PRN medications were informed by resident request, interpretation of resident-specific actions, training and experience, and setting-specific practices. The theme, learning about your residents, was consistent across settings. Implications: By administering PRN medications, medication aides play an important role in the daily care and comfort of AL residents with dementia. Policy makers need information about whether to permit unlicensed staff to administer medications and the level of training to require. This research suggests that training should recognize the tacit knowledge of practicing medication aides. Despite the role that PRN medications can play in the daily comfort and well-being of AL residents, little is known about as-needed medications prescribed versus those actually used across settings; also needed is an understanding of how other health professionals are involved in treatment plans that include medications.