Insomnia is a major health problem, with significant psychological, health, and economic consequences. Studies have demonstrated that cognitive-behavioural therapy can effectively treat insomnia; however, treatment availability is limited by many factors, including a lack of trained clinicians. One potential way to overcome these barriers is to use the Internet to deliver treatment. Toward this aim, we developed a self-guided, interactive, tailored Internet intervention for adults with insomnia (SHUTi: Sleep Healthy Using The Internet). The current paper provides a detailed description of SHUTi and examines users' perceptions of the intervention's usefulness and effectiveness. The study was part of a larger randomised controlled trial (RCT) to test the efficacy of SHUTi, but findings in this paper are based only on the 21 participants who completed the post-assessment after using SHUTi. The overwhelming majority rated SHUTi as convenient, understandable, and useful. Nearly all (95%) indicated that the program had at least somewhat improved their sleep, sleep efficiency, and overall quality of life. Ninety percent perceived the intervention as effective and predicted it would be effective in producing a long-term cure. Although these results were based on a small sample, they provide encouraging evidence of the potential for Internet interventions to be accepted by patients.