BACKGROUND: Physician work intensity (WI) during office-based patient care affects quality of care and patient safety as well as physician job-satisfaction and reimbursement. Existing, brief work intensity measures have been used in physician studies, but their validity in clinical settings has not been established. OBJECTIVES: Document and describe subjective and temporal WI dimensions for physicians in office-based clinical settings. Examine these in relation to the measurement procedures and dimensions of the SWAT and NASA-TLX intensity measures. DESIGN: A focused ethnographic study using interviews and direct observations. PARTICIPANTS: Five family physicians, 5 general internists, 5 neurologists, and 4 surgeons. METHODS: Through interviews, each physician was asked to describe low and high intensity work responsibilities, patients, and events. To document time and task allotments, physicians were observed during a routine workday. Notes and transcripts were analyzed using the editing method in which categories are obtained from the data. RESULTS: WI factors identified by physicians matched dimensions assessed by standard, generic instruments of work intensity. Physicians also reported WI factors outside of the direct patient encounter. Across specialties, physician time spent in direct contact with patients averaged 61% for office-based services. CONCLUSIONS: Brief work intensity measures such as the SWAT and NASA-TLX can be used to assess WI in the office-based clinical setting. However, because these measures define the physician work "task" in terms of effort in the presence of the patient (ie, intraservice time), substantial physician effort dedicated to pre- and postservice activities is not captured.