During a three-month study period, visitors to an online decision aid (DA) for attention deficit hyperactivity disorder (ADHD) were invited to complete an online questionnaire before and after working through the DA. Some 75,000 unique visitors found their way to the page on DAs, although fewer than 1 in 10 visited the DA for ADHD, staying there for about six minutes on average and using 8–9 clicks to navigate. A total of 195 people completed the first questionnaire (a response rate of about 3%). Only 12 of the respondents to the first questionnaire (6%) completed the second questionnaire. There was no significant effect of the DA as measured by three decisional outcome measures. Respondents moderately appreciated the information received. Even though the DA was constructed according to evidence-based guidelines and International Patient Decision Aids Standards wherein expert and patient involvement are assured, these preliminary results suggest that the online DA for ADHD needs further work to support the decision-making process of parents with regard to the most appropriate treatment for their child.