The aim of this investigation was to study pharmacological treatment in relation to asthma severity among patients visiting an asthma web site on the Internet. The study comprised 650 subjects from 30 countries with self-reported asthma that participated in an Internet based patient survey. The survey was posted on the web site Asthma Information Centre (www.mdnet.de). Moderate or severe night cough or wheezing was reported by 43% and activity limitation by 55% of the asthmatics. Short-acting beta-agonists were used by 67% and inhaled steroids by 59%. The use of short-acting beta-agonists decreased with age, whereas the use of inhaled steroids, long-acting beta-agonists and antileukotrienes was lowest in the youngest (0-20 years) and highest age groups (> 60 years). The use of short-acting beta-agonists increased, and the use of inhaled steroids decreased with the severity of nocturnal symptoms (p < 0.01). Side effects were most often reported for oral beta-agonists (42%) and least often for antileukotrienes (9%). We conclude that despite problems with selection and external validity, an online asthma survey produces results that agree highly with more resource-demanding surveys. We find that many asthmatics have a low level of asthma control, and the survey indicates that underuse of inhaled steroids is one of the reasons why the goals set up in asthma guidelines so far have not been reached.