Many people with functional gastrointestinal disorders (FGIDs) face significant barriers in accessing psychological treatments that are known to reduce symptoms and their psychological sequelae. This study examined the feasibility and initial outcomes of a transdiagnostic and internet-delivered cognitive behaviour therapy (iCBT) intervention, the Chronic Conditions Course, for adults with functional gastrointestinal disorders (FGIDs). A single-group feasibility open trial design was employed and administered to twenty seven participants. The course ran for 8 weeks and was provided with weekly contact from a Clinical Psychologist. Seventy percent of participants completed the course within the 8 weeks and 81.5% provided data at post-treatment. High levels of satisfaction were observed and relatively little clinician time (M = 42.70 min per participant; SD = 46.25 min) was required. Evidence of clinical improvements in FGID symptoms (ds ≥ 0.46; avg. improvement ≥21%), anxiety symptoms (ds ≥ 0.99; avg. improvement ≥42%), and depression symptoms (ds ≥ 0.75; avg. improvement ≥35%) were observed, which either maintained or continued to improve to 3-month follow-up. Evidence of improvement was also observed in pain catastrophising and mental-health related quality of life, but not physical-health related quality of life. These findings highlight the potential value of transdiagnostic internet-delivered programs for adults with FGIDs and support for the conduct of larger-scale controlled studies.