The National Asthma Education and Prevention Program (NAEPP) and the American Thoracic Society provide guidelines stating that physicians should use spirometry in the diagnosis and management of asthma. The aim of this study was to evaluate the trends, over a 10-year period, in the utilization of spirometry in patients newly diagnosed with asthma. We hypothesized that spirometry use would increase in physicians who care for asthma patients, especially since 2007, when the revised NAEPP guidelines were published.