This study investigated the influence of drug-company funding on websites about attention-deficit hyperactivity disorder (ADHD). Websites in the top 60 for either Google or Yahoo!Xtra with information about causation and treatment were analysed. Likert scales, based on those used in previous similar studies, were developed to rate aetiological explanations and recommended treatment approaches, on a dimension from psycho-social to biological. Overall, the quality of information on websites was poor with a strong bias towards bio-genetic aetiological explanations of ADHD. Twenty-one of the 57 websites (37%) were funded by drug companies. The drug-company funded (DCF) websites were significantly more likely than non-DCF websites to recommend medication rather than psycho-social treatments. The selective lack of consideration of psycho-social treatments by DCF websites is discussed in relation to the relevant research literature, including the evidence in favour of a multimodal approach. The findings, which are consistent with previous similar studies in relation to websites about adult mental health problems, confirm that the pharmaceutical industry is seeking to influence public opinion via the internet.