Clinical pathways are useful tools in improving the quality of care of patients treated in hospitals. Gastroenteritis is a short, self-limiting, but common illness of childhood associated with significant costs to the community. The authors assessed the impact of a clinical pathway on investigation ordering in children with gastroenteritis. A retrospective analysis of 2 cohorts of children was performed before (n=1498) and after (n=1252) the introduction of a clinical pathway. Children admitted to hospital with a diagnosis of gastroenteritis were assessed as to the type of pathology tests ordered. Further outcomes measured were rates of admission, emergency department presentations, average length of stay, and direct costs. Subset analysis was undertaken on the initial cohort of patients who had a full blood count as part of their initial assessment. Full blood count was more likely to be performed prior to the introduction of the pathway(77.1%) than after pathway introduction (66.8%; P<.004). Urine microscopy and culture also was significantly decreased from 56.3% to 40.4% (P<.0005). Median patient costs were reduced from $1228 to $752 following pathway introduction (P<.0001); however, rates of admission were increased from 18.6% to 28.8% (P<.0001). Length of stay decreased but was not statistically significant. Full blood count results in the subset analysis revealed that the measurement of a full blood count had no impact on management. Thus, a clinical pathway contributed to more rational ordering of pathology tests and lowered the costs to a hospital of caring for patients with this common illness.