Providing smokers with personal genetic test results indicating increased lung cancer risk may increase uptake of effective smoking cessation services. Using the internet may increase reach and enable real-time assessment of how people process genetic risk information away from the clinic setting. We therefore explored smokers' responses to Web-delivered GSTM1 genetic test results indicating higher or lower lung cancer risk. Participants were smokers (n = 44) biologically related to patients with newly diagnosed lung cancer. Measures were assessed at baseline, before and immediately after receipt of online genetic test results, and at 6-month follow-up. Outcomes included accurate comprehension of results, regret about being tested, cessation-related cognitions (e.g., perceived response efficacy), and uptake of free smoking cessation services (nicotine replacement therapy, printed self-help materials, telephone counseling sessions). Twenty-two "relative smokers" received a GSTM1-missing (higher risk) and 22 a GSTM1-present (lower risk) result. All relative smokers with GSTM1-missing results and 55% of those with GSTM1-present results accurately interpreted their results. No relative smokers regretted having taken the test. Relative smokers receiving GSTM1-missing results reported lower confidence that quitting could reduce lung cancer risk (perceived response efficacy) than those receiving GSTM1-present results. There were no other significant between-group differences. Uptake of smoking cessation services was high (e.g., 91% nicotine replacement therapy uptake). Genetic test results may not influence uptake of free smoking cessation services because of ceiling effects. Further research is needed to determine the risks and benefits of Web-based disclosure of genetic test results.