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.A service-based effectiveness randomised waiting list control trial examined the impact of an internet-delivered CBT intervention, Calming Anxiety, amongst Irish university students (N=137). Primary outcome was self-reported GAD and secondary outcomes included depression and work and social functioning.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.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.