Electronic ordering systems have the potential to enhance the efficient utilisation of pathology services. The aim of this study was to assess the effect of electronic pathology ordering on repeat test ordering for paediatric patients (ages 0 to 18 years) who were in intensive care units (ICUs) and non-ICU wards. The dataset described 85,728 pathology tests ordered for 5,073 children before and after the implementation of electronic ordering. This study showed that, for children in ICUs, the repeat test order rate was significantly lower for electronic orders than for paper-based orders. Similarly, the rate of repeat tests ordered within short intervals (up to 23-hours), for children older than one-year in non-ICU wards, was lower for electronic ordering than for paper ordering. The proportion of repeat tests occurring within one-hour of the previous test was consistently lower for tests ordered using electronic ordering than it was for tests ordered using the paper based system for patients older than one-year in all wards and for patients under one-year in ICUs. These results suggest that features of the electronic system, including alerts about previously ordered tests and the availability of information about previous orders, can help clinicians to identify and reduce unnecessary repeat tests.