Doctors often complain about the burden of administrative work, but few studies have quantified how much time clinicians devote to administrative tasks. We quantified the time U.S. physicians spent on administrative tasks, and its relationship to their career satisfaction, based on a nationally representative survey of 4,720 U.S. physicians working 20 or more hours per week in direct patient care. The average doctor spent 8.7 hours per week (16.6% of working hours) on administration. Psychiatrists spent the highest proportion of their time on administration (20.3%), followed by internists (17.3%) and family/general practitioners (17.3%). Pediatricians spent the least amount of time, 6.7 hours per week or 14.1 percent of professional time. Doctors in large practices, those in practices owned by a hospital, and those with financial incentives to reduce services spent more time on administration. More extensive use of electronic medical records was associated with a greater administrative burden. Doctors spending more time on administration had lower career satisfaction, even after controlling for income and other factors. Current trends in U.S. health policy--a shift to employment in large practices, the implementation of electronic medical records, and the increasing prevalence of financial risk sharing--are likely to increase doctors' paperwork burdens and may decrease their career satisfaction.