Increasing numbers of people are turning to the Internet for health advice despite reports that sites vary in terms of their quality. How do they decide whether or not to trust the advice they find online? A staged model of trust development is proposed and tested here in a longitudinal study in which fifteen women faced with decisions concerning the menopause and hormone replacement therapy (HRT) were observed while searching the Internet for information and advice over four consecutive weeks and then kept diaries over a six-month follow-up period. The women were all resident in the North-East of England and were recruited through advertisements in the local media. The study provided general support for a three-stage model of trust in which participants firstly engaged in rapid heuristic processing of information, efficiently sifting and rejecting general sales sites and portals but sometimes rejecting high-quality content because of poor design. Well-designed sites were then effectively interrogated for credible and personalized content before being designated trustworthy. The women appeared to act much like 'scientists' using web material to generate and test hypotheses and theories about HRT, although their capacity to deal with certain forms of risk information was limited. They subsequently reported integrating online advice with offline advice from friends, family and physicians in order to be fully confident in their final decisions. Women felt that the Internet influenced their decision-making and improved communications with physicians. Personalized stories from like-minded others improved trust perceptions. Despite the use of the Internet the physician was still seen as the primary source of information and advice.