PURPOSE A substantial proportion of adult patients with asthma have inadequately controlled symptoms despite the availability of effective treatment. The Asthma Control Questionnaire (ACQ) can be used to discriminate between asthma patients with well- and suboptimally controlled asthma symptoms. The objective of this study was to investigate whether a postal mailing of the ACQ can be used to identify asthma patients with suboptimal symptom control in family practice. METHODS In this observational study, we sent 434 asthma patients from 6 Dutch family practices an ACQ by mail to measure control of their asthma symptoms. Both respondents and nonrespondents were characterized by information gathered from their medical records. Patients with an ACQ sum score (total score) of greater than 3 were considered to have suboptimally controlled asthma symptoms. RESULTS The response rate was 77%. Respondents were more likely than non- respondents to be female and to use asthma medication. The mean ACQ sum score of the respondents was 5.2. Of this group, 53.4% (95% confidence interval, 48.0%-58.8%) had suboptimally controlled asthma symptoms. Of the 168 respondents who had not visited their family physician in the 2 years before the study, 42.9% (95% confidence interval, 35.4%-50.4%) had inadequate asthma symptom control. CONCLUSIONS Our results show that a postal mailing of the ACQ is an effective approach for tracing asthma patients who need medical attention. It also traces patients who would otherwise not have consulted their family physician. The ACQ seems to be a useful starting point for health care professionals in family practice to improve the level of asthma symptom control in their patient population.