The aim of this study was to investigate the efficacy of an internet-based, therapist assisted, parent-focussed, CBT program for preschoolers with anxiety disorders. Fifty-two children aged 3-6 years were randomly allocated into internet treatment (NET) and waitlist control (WLC) groups. Parents completed diagnostic interviews and online questionnaires at pre-treatment, post-treatment and 6-month follow-up. Results at post-treatment showed a significantly greater reduction in clinical severity, anxiety symptoms and internalising behaviour, as well as a greater increase in overall functioning for children in the NET compared to the WLC condition. However, group differences were not evident from pre- to post-treatment on the percentages of children who lost their primary anxiety diagnosis or who lost all anxiety diagnoses. At post-treatment for the completer sample, 39.1% of the NET children compared to 25.9% of the WLC were free of their primary diagnosis. At 6-month follow-up, treatment gains were maintained in the case of overall functioning and further improved upon with respect to clinical severity, anxiety symptoms and internalising behaviour. By 6-month follow-up for the completer sample, 70.6% of children were free of their primary diagnosis. The results suggest that an internet program for preschool anxiety is feasible, efficacious and well received by parents.