Sleep problems are treatable causes of morbidity and mortality, but little is known about how often the history fundamental to diagnosis is obtained. We recorded the frequency of sleep histories during encounters with simulated patients by 20 experienced primary care practitioners, 23 uninstructed medical interns, and 22 interns who had previous instruction about sleep disorders. Sleep histories were uncommonly obtained by uninstructed physicians (0% of practitioners, 13% of interns), but trained interns more often (81.8%) asked about sleep. If sleep problems are to be prioritized, major changes in physician education and behaviors are essential. Focused instruction about sleep influences physician behavior.