BackgroundThe NHS emergency and urgent care system is under pressure as demand for services increases each year. NHS 111 is a telephone triage service designed to provide advice and signposting to appropriate services for people with urgent health-care problems. A new service, NHS 111 Online, has been introduced across England as a digital alternative that can be accessed using a website or a smartphone application. The effects and usefulness of this service are unknown.ObjectivesTo explore the impact of NHS 111 Online on the related telephone service and urgent care system activity and the experiences of people who use those services.Design and methodsA mixed-methods design of five related work packages comprising an evidence review; a quantitative before-and-after time series analysis of changes in call activity (18/38 sites); a descriptive comparison of telephone and online services with qualitative survey (telephone,n = 795; online,n = 3728) and interview (32 participants) studies of service users; a qualitative interview study (16 participants) of staff; and a cost–consequences analysis.ResultsThe online service had little impact on the number of triaged calls to the NHS 111 telephone service. For every 1000 online contacts, triaged telephone calls increased by 1.3% (1.013, 95% confidence interval 0.996 to 1.029;p = 0.127). Recommendations to attend emergency and urgent care services increased between 6.7% and 4.2%. NHS 111 Online users were less satisfied than users of the telephone service (50% vs. 71%;p < 0.001), and less likely to recommend to others (57% vs. 69%;p < 0.001) and to report full compliance with the advice given (67.5% vs. 88%;p < 0.001). Online users were less likely to report contacting emergency services and more likely to report not making any contact with a health service (31% vs. 16%;p < 0.001) within 7 days of contact. Thirty-five per cent of online users reported that they did not want to use the telephone service, whereas others preferred its convenience and speed. NHS 111 telephone staff reported no discernible increase or decrease in their workload during the first year of operation of NHS 111 Online. If online and telephone services operate in parallel, then the annual costs will be higher unless ≥ 38% of telephone contacts move to online contacts.ConclusionsThere is some evidence that the new service has the potential to create new demand. The service has expanded significantly, so it is important to find ways of promoting the right balance in numbers of people who use the online service instead of the telephone service if it is to be effective. There is a clear need and preference by some people for an online service. Better information about when to use this service and improvements to questioning may encourage more uptake.LimitationsThe lack of control arm means that impact could have been an effect of other factors. This work took place during the early implementation phase, so findings may change as the service expands.Future workFurther development of the online triage process to make it more ‘user friendly’ and to enable users to trust the advice given online could improve use and increase satisfaction. Better understanding of the characteristics of the telephone and online populations could help identify who is most likely to benefit and could improve information about when to use the service.Trial registrationCurrent Controlled Trials ISRCTN51801112.FundingThis project was funded by the National Institute for Health Research (NIHR) Health Services and Delivery Research programme and will be published in full inHealth Services and Delivery Research; Vol. 9, No. 21. See the NIHR Journals Library website for further project information.