Paediatric intensive care patients are at high risk for prescription errors due to the more complex process of medication prescribing. Clinical decision support systems (CDSS) have shown good results in effectively reducing prescription errors. A specific dosing CDSS was developed that can check and suggest normal dose, dose limits and administration frequencies. This study aimed to assess the effect of this CDSS on protocol deviation (as measure of prescription error) types and frequency in a paediatric intensive care unit (PICU).A retrospective observational study was conducted evaluating 9342 prescriptions in a 4-month period before and after the implementation of a CDSS in the PICU of the University Medical Center Utrecht. Medication forms were reviewed to identify protocol deviations (and therefore possible prescription errors). The incidence and nature of deviations from evidence-based protocols that were unintended and needed to be adjusted, were determined.In the period before the dosing CDSS, we identified 45 protocol deviations in 5034 prescriptions (0.89%), 28 of which could not be justified (0.56%) and 11 needed to be adjusted (0.22%). In the period after the implementation of the CDSS, there were 21 protocol deviations in 4308 prescriptions (0.49%) of which ten without a valid reason (0.23%) of which two were adjusted (0.05%).The specific dosing CDSS was able to significantly reduce unintentional prescription dose deviations and the number of prescriptions that needed to be adjusted, in an existing low incidence situation.