Patients' expectations and the role they play in medical care are increasingly considered to be important, but the factors that influence these expectations have not been well studied. To examine the factors that influence patients' expectations for care in office practice. Qualitative inquiry nested within a large clinical survey. Three general internal medicine practices in one mid-sized city in northern California. 688 patients visiting their internists' offices were surveyed (response rate, 86%); 88 patients who reported one or more omissions of care on a post-visit questionnaire and were available for a telephone interview 1 to 7 days after the visit were included in the qualitative inquiry. Proportion of surveyed patients who reported one or more omissions of care, and qualitative analysis of the sources of patients' expectations, as determined from the telephone interviews. Interviews focused on the sources of expectations and perceptions of omission. Using an iterative process and working by consensus, investigators developed coding categories on a randomly selected 50% of the transcripts. The other 50% of the sample was used for validation. The 125 patients who had unmet expectations perceived omissions that were related to physician preparation for the visit (23%), history taking (26%), physical examination (30%), diagnostic testing (28%), prescription of medication (19%), referral to specialists (26%), and physician-patient communication (15%). Unmet expectations were shaped by patients' current somatic symptoms (intensity of symptoms, functional impairment, duration of symptoms, and perceived seriousness of symptoms) (74%); perceived vulnerability to illness (related to age, family history, personal lifestyle, or previously diagnosed conditions) (50%); past experiences (personal or familial) with similar illnesses (42%); and knowledge acquired from physicians, friends, family, or the media (54%). Patients' expectations for care are derived from multiple sources; their complexity should discourage simple schemes for "demand management." Nevertheless, the results of this study may help physicians to take a more empathetic stance toward their patients' requests and to devise more successful strategies for clinical negotiation.