Background: Low mobility is common during hospitalization and is associated with adverse outcomes. Understanding barriers to the maintenance or improvement of mobility is important to the development of successful interventions. Objectives: To identify barriers to mobility during hospitalization from the perspectives of older patients and their primary nurses and physicians, to compare and contrast the perceived barriers among these groups, and to make a conceptual model. Design: Qualitative interviews analyzed and interpreted using a grounded theory approach. Setting: Medical wards of a university hospital. Participants: Twenty-nine participants - 10 patients ≥ 75 years, 10 nurses, and 9 resident physicians. Measurements: Participants were interviewed using a semistructured interview guide, with similar questions for patients and health care providers. Interviews were audiotaped, transcribed, and reviewed for common themes by independent reviewers. Perceived barriers to mobility were identified, and their nature and frequency were examined for each respondent group. Results: Content analysis identified 31 perceived barriers to increased mobility during hospitalization. Barriers most frequently described by all 3 groups were: having symptoms (97%), especially weakness (59%), pain (55%), and fatigue (34%); having an intravenous line (69%) or urinary catheter (59%); and being concerned about falls (79%). Lack of staff to assist with out-of-bed activity was mentioned by patients (20%), nurses (70%), and physicians (67%). Unlike patients, health care providers attributed low mobility among hospitalized older adults to lack of patient motivation and lack of ambulatory devices. Conclusions: Recognizing and understanding perceived barriers to mobility during hospitalization of older patients is an important first step toward developing successful interventions to minimize low mobility. © 2007 Society of Hospital Medicine.