Introduction: Randomised controlled trials have shown that internet-delivered cognitive behavioural treatment (iCBT) is an effective treatment for health anxiety, but the effectiveness of these programs in routine care has not been investigated. This study examined the effectiveness of iCBT for health anxiety symptoms in routine care settings in the community. Methods: Using an open-trial design, we investigated adherence to, and effectiveness of a 6-lesson iCBT program for health anxiety symptoms amongst individuals (n=391, mean age 41 years, 64% female) who enrolled in the program either self-guided (n=312) or under the supervision of community clinicians (general practitioners, psychologists and other allied health professionals) (n=79). Primary outcome was health anxiety severity on the Short Health Anxiety Inventory (SHAI), and secondary outcomes were depression severity on the Patient Health Questionnaire 9-item (PHQ-9) (depression) and distress (Kessler-10: K-10). Results: Adherence to the iCBT program was modest (45.6% in the clinician-supervised group, 33.0% in the unguided group), but within-subjects effect sizes were large (SHAI: g=1.66, 95%CI: 1.45–1.88; PHQ-9: g=1.12, 95%CI: 0.92–1.32; K-10: g=1.35, 95%CI: 1.15–1.56). Limitations: No control group, lack of follow-up data. Conclusions: iCBT is an effective treatment for health anxiety symptoms in routine care, but methods to increase adherence are needed to optimise benefits to participants. Randomised controlled effectiveness trials with long-term follow-up are needed.