The purpose of this paper is to document everyday practices by which hospitalist physicians negotiate barriers to effective teamwork. Ethnographic observation with a sample of hospitalists chosen to represent a range of hospital and practice types. Hospitals rely on effective, interprofessional teamwork but typically do not support it. Hospitalist physicians must bridge the internal boundaries within their hospitals to coordinate their patients' care, but they face challenges - scattered patients, fragmented information, uncoordinated teams, and unreliable processes - that can impact the timeliness and safety of care. Hospitalists largely rely on personal presence and memory to deal with these challenges. Some invent low-tech supports for teamwork, but these are typically neither tested nor shared with others. Formal support for teamwork, primarily case management rounds, is applied unevenly and may not be respected by all team members. The findings are drawn from observation over a limited period of time with a small, purposefully chosen sample of physicians and hospitals. Practical implications - Hospitals must recognize the issues hospitalists and other providers face, evaluate and disseminate supports for teamwork, and make interprofessional teamwork a core feature of hospital design and evaluation. The authors show the nuances of how hospitalists struggle to practice teamwork in a challenging context, and how the approaches they take (relying on memory and personal presence) do not address, and may actually contribute to, the system-level problems they face.