Article history: Received 29 April 2016 Received in revised form 26 October 2016 Accepted 27 October 2016 Available online 29 October 2016 Background: Cognitive behavioural therapy is one of the main and preferred treatments for generalized anxiety disorder. Numerous barriers can hinder an individual from seeking or receiving appropriate treatment; internet-delivered CBT interventions offer a relatively new means of increasing access to treatment. Methods: A service-based effectiveness randomisedwaiting list control trial examined the impact of an internetdelivered CBT intervention, Calming Anxiety, amongst Irish university students (N=137). Primary outcomewas self-reported GAD and secondary outcomes included depression and work and social functioning. Results: Analyses returned inconclusive results. Both treatment and waiting list conditions displayed significant decreases in anxiety symptoms post-treatment, but we did not observe a significant between-group effect (p = 0.076). Significant within-group differences from pre to post time points were observed for depression (BDI-II) and work and social functioning (WASA), and between group differences were also significant for depression (d = 0.46) and functioning (d = 0.36). Both groups demonstrated cases of remission and recovery from anxiety, however differences in the number of cases reaching clinically meaningful change between conditions were non-significant. Conclusions: Several explanations regarding the results are presented, examining issues related to active waiting lists, study limitations and treatment expectancies. Trial registration: Current Controlled Trials ISRCTN16303842. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).