Objectives To assess the effectiveness and cost-utility of a multifaceted eHealth strategy compared to usual care in improving patients' back pain beliefs, and in decreasing disability and absenteeism. Design Stepped-wedge cluster randomised trial with parallel economic evaluation. Setting Dutch primary healthcare. Participants Patients diagnosed with non-specific low back pain by their general practitioner or physiotherapist. Patients with serious comorbidities or confirmed pregnancy were excluded. 779 patients were randomised into intervention group (n=331, 59% female; 60.4% completed study) or control group (n=448, 57% female; 77.5% completed study). Interventions The intervention consisted of a multifaceted eHealth strategy that included a (mobile) website, digital monthly newsletters, and social media platforms. The website provided information about back pain, practical advice (eg, on self-management), working and returning to work with back pain, exercise tips, and short video messages from healthcare providers and patients providing information and tips. The control consisted of a digital patient information letter. Patients and outcome assessors were blinded to group allocation. Primary and secondary outcome measures The primary outcome was back pain beliefs. Secondary outcome measures were disability and absenteeism, and for the preplanned economic evaluation quality of life and societal costs were measured. Results There were no between-group differences in back pain beliefs, disability, or absenteeism. Mean intervention costs were €70-and the societal cost difference was €535-in favour of the intervention group, but no significant cost savings were found. The incremental cost-effectiveness ratio indicated that the intervention dominated usual care and the probability of cost-effectiveness was 0.85 on a willingness-to-pay of €10.000/quality adjusted life year (QALY). Conclusions A multifaceted eHealth strategy was not effective in improving patients' back pain beliefs or in decreasing disability and absenteeism, but showed promising cost-utility results based on QALYs. Trial registration number NTR4329.