ABSTRACT: BACKGROUND:Type 2 diabetes mellitus is one of the most common long-term conditions, and costs health services approximately 10% of their total budget. Active self-management by patients improves outcomes and reduces health service costs. While the existing evidence suggested that uptake of self-management education was low, the development of internet-based technology might improve the situation. OBJECTIVE:To establish the cost-effectiveness of a Web-based self-management program for people with type 2 diabetes (HeLP-Diabetes) compared to usual care. METHODS:An incremental cost-effectiveness analysis was conducted, from a National Health Service and personal and social services perspective, based on data collected from a multi-center, two-arm individually randomized controlled trial over 12 months. Adults aged 18 or over with a diagnosis of type 2 diabetes and registered with the 21 participating general practices (primary care) in England, UK, were approached. People who were unable to provide informed consent or to use the intervention, terminally ill, or currently participating in a trial of an alternative self-management intervention, were excluded. The participants were then randomized to either usual care plus HeLP-Diabetes, an interactive, theoretically-informed Web-based self-management program, or to usual care plus access to a comparator website containing basic information only. The participants' intervention costs and wider health care resource use were collected as well as two health-related quality of life measures: the Problem Areas in Diabetes (PAID) Scale and EQ-5D-3L. EQ-5D-3L was then used to calculate quality-adjusted life years (QALYs). The primary analysis was based on intention-to-treat, using multiple imputation to handle the missing data. RESULTS:In total, 374 participants were randomized, with 185 in the intervention group and 189 in the control group. The primary analysis showed incremental cost-effectiveness ratios of £58 (95% CI -411 to 587) per unit improvement on PAID scale and £5550 (95% CI -21,077 to 52,356) per QALY gained by HeLP-Diabetes, compared to the control. The complete case analysis showed less cost-effectiveness and higher uncertainty with incremental cost-effectiveness ratios of £116 (95% CI -1299 to 1690) per unit improvement on PAID scale and £18,500 (95% CI -203,949 to 190,267) per QALY. The cost-effectiveness acceptability curve showed an 87% probability of cost-effectiveness at £20,000 per QALY willingness-to-pay threshold. The one-way sensitivity analyses estimated 363 users would be needed to use the intervention for it to become less costly than usual care. CONCLUSIONS:Facilitated access to HeLP-Diabetes is cost-effective, compared to usual care, under the recommended threshold of £20,000 to £30,000 per QALY by National Institute of Health and Care Excellence. TRIAL REGISTRATION:International Standard Randomized Controlled Trial Number (ISRCTN) 02123133; http://www.controlled-trials.com/ISRCTN02123133 (Archived by WebCite at http://www.webcitation.org/6zqjhmn00).