BACKGROUND: Patients who visit online support groups benefit in various ways. Results of our earlier study indicated that participation in online support groups had a profound effect on the participants' feelings of "being empowered." However, most studies of online patient support groups have focused on the members of these groups who actively contribute by sending postings (posters). Thus far, little is known about the impact for "lurkers" (ie, those who do not actively participate by sending postings). OBJECTIVE: In the present study, we explored if lurkers in online patient support groups profit to the same extent as posters do. METHODS: We searched the Internet with the search engine Google to identify all Dutch online support groups for patients with breast cancer, fibromyalgia, and arthritis. Invitations to complete an online survey were sent out by the owners of 19 groups. In the online questionnaire, we asked questions about demographic and health characteristics, use of and satisfaction with the online support group, empowering processes, and empowering outcomes. The online questionnaire was completed by 528 individuals, of which 109 (21%) identified themselves as lurkers. RESULTS: Lurkers (mean age 47 years) were slightly older than active participants (mean age 43 years, P = .002), had a shorter disease history (time since diagnosis 3.7 years vs 5.4 years, P = .001), and reported lower mental well-being (SF 12 subscore 37.7 vs 40.5, P = .004). No significant differences were found in other demographic variables. Posters indicated visiting the online support groups significantly more often for social reasons, such as curiosity about how other members were doing, to enjoy themselves, as a part of their daily routine (all P < .001), and because other members expected them to be there (P = .003). Lurkers and posters did not differ in their information-related reasons for visiting the online support group. Lurkers were significantly less satisfied with the online support group compared to posters (P < .001). With regard to empowering processes such as "exchanging information" and "finding recognition," lurkers scored significantly lower than posters. However, lurkers did not differ significantly from posters with regard to most empowering outcomes, such as "being better informed," "feeling more confident in the relationship with their physician," "improved acceptance of the disease," "feeling more confident about the treatment," "enhanced self-esteem," and "increased optimism and control." The exception was "enhanced social well-being," which scored significantly lower for lurkers compared to posters (P < .001). CONCLUSION: Our study revealed that participation in an online support group had the same profound effect on lurkers' self-reported feelings of being empowered in several areas as it had on posters. Apparently, reading in itself is sufficient to profit from participation in an online patient support group.