The number of hospital-based physicians, or hospitalists, in the United States has grown rapidly, yet no published data have characterized hospitalists or their practices. A self-administered questionnaire was used to describe 1) the features of hospitalists, 2) the hospitals in which they practice, and 3) the practice of inpatient medicine. The questionnaire contained 48 questions that covered four domains: demographic information about the respondent, the clinical and nonclinical workload and responsibilities of the respondent, organizational and financial aspects of the respondent's practice, and the respondent's satisfaction and his or her perception of the reaction of other physicians and nurses to the hospitalist system. The overall response rate was 57%. Data are reported on 372 surveys. Respondents were young and most were men, and only 48% had practiced hospital-based medicine for more than 2 years. Eighty-nine percent of respondents were internists; of these, 51% were generalists and 38% were subspecialists. Most hospitalists limited their practices to the inpatient setting, but 37% practiced outpatient general internal medicine or subspecialty medicine in a limited capacity. In addition to providing care for inpatients, 90% of hospitalists were engaged in consultative medicine. Quality assurance and practice guideline development were the most frequently reported nonclinical activities (53% and 46%, respectively). Small group practices (31%) and staff-model health maintenance organizations (25%) were the most common practice settings, and 78% of participants were reimbursed through salary. Financial incentives were common (43%) but modest. Accurate information about hospitalists and their practices will be important to clinicians, educators, researchers, and policymakers as the hospitalist movement continues to grow.