Treatment guidelines recognize the importance of achieving and maintaining asthma control. This study was designed to assess the prevalence of asthma control in a representative U.S. population. A survey regarding asthma and associated symptoms was sent to a representative national sample of 134,401 households managed by the National Family Opinion WorldGroup from May to July 2007. Subjects >or=18 years with current asthma were identified and completed the Asthma Control Test (ACT), a brief validated self-administered survey that assesses asthma control. Subjects with an ACT score of >19 have been defined as having well-controlled asthma (WCA) and those with a score of <or=19 were defined as having not well-controlled asthma (NWCA). The prevalence of WCA was identified for the total population as well as subjects who currently were only using albuterol to control asthma symptoms. In addition, the frequency of past asthma exacerbations was studied and correlated with ACT. Surveys were returned by 81,505 households (61% return rate). A total of 10,139 adults self-reported having asthma and completed the ACT. Forty-one percent of these had NWCA and 39% of the subjects using albuterol as the only asthma medication had NWCA. Fifty-eight percent of subjects with NWCA in the total population had an asthma-related exacerbation (asthma-related oral corticosteroid use, emergency department, or hospitalization) in the previous year compared with 24% of subjects with WCA. This large representative national asthma sample using a validated asthma control instrument identified >40% of subjects with NWCA. In addition, subjects using albuterol monotherapy, who would be expected to have mild asthma and thus be well controlled, had a similar high prevalence of NWCA.