OBJECTIVES: This study attempted to determine if select patient and physician demographic variables are predictors of the prescribing of asthma pharmacotherapy in the ambulatory patient population of the United States. Another aim of this study was to evaluate if physician prescribing behavior of asthma pharmacotherapy was in compliance with the recommendations of the National Heart, Lung & Blood Institute's National Asthma Education and Prevention Program Expert Panel 2 national asthma guidelines. METHODS: This study was a retrospective cross-sectional study that used data from the National Ambulatory Medical Care Survey (NAMCS) from 1998 through 2004. The weighted population sample size of the study was 82,020,318 patients. Specific patient demographic variables, physician demographic variables and asthma medications prescribed were extracted from the dataset and analyzed using logistic regression procedures. RESULTS: The major finding from the study was that physicians did not seem to be adhering to the EPR-2 pharmacotherapy guidelines. Another major finding from this study was the fact that there were vulnerable sub-populations of asthma patients that were receiving sub-optimal asthma pharmacotherapy. It was also found that patients who were non-white and non-African American were also less likely to receive optimal asthma pharmacotherapy (all p<0.05). The majority of these patients were of Asian origin. These individuals were less likely to be prescribed controller medications and more likely to be prescribed SABA agents when compared to whites. Patient status, physician specialty, ownership status and physician employment status were important variables in certain aspects of asthma pharmacotherapy. CONCLUSION: It appears that a more concerted effort needs to be undertaken to improve physician adherence to the EPR-2 guidelines, especially in the prescribing of asthma pharmacotherapy. There is also a need to address the disparities observed in the prescribing of asthma pharmacotherapy in vulnerable, underserved populations.