Background: Management of children with minor blunt head trauma often includes a period of observation to determine the need for cranial computed tomography (CT). Our objective was to estimate the effect of planned observation on CT use for each Pediatric Emergency Care Applied Research Network (PECARN) traumatic brain injury (TBI) risk group among children with minor head trauma. Methods: This was a secondary analysis of a prospective observational study at 10 emergency departments (EDs) in Australia and New Zealand, including 18,471 children ' 18 years old, presenting within 24 hours of blunt head trauma, with Glasgow Coma Scale scores of 14 to 15. The planned observation cohort was defined by those with planned observation and no immediate plan for cranial CT. The comparison cohort included the rest of the patients who were either not observed or for whom a decision to obtain a cranial CT was made immediately after ED assessment. The outcome clinically important TBI (ciTBI) was defined as death due to head trauma, neurosurgery, intubation for ' 24 hours for head trauma, or hospitalization for ≥ 2 nights in association with a positive cranial CT scan. We estimated the odds of cranial CT use with planned observation, adjusting for patient characteristics, PECARN TBI risk group, history of seizure, time from injury, and hospital clustering, using a generalized linear model with mixed effects. Results: The cranial CT rate in the total cohort was 8.6%, and 0.8% had ciTBI. The planned observation group had 4,945 (27%) children compared to 13,526 (73%) in the no planned observation group. Cranial CT use was significantly lower with planned observation (adjusted odds ratio [OR] = 0.2, 95% confidence interval [CI] = 0.1 to 0.1), with no difference in missed ciTBI rates. There was no difference in the odds of cranial CT use with planned observation for the group at very low risk for ciTBI (adjusted OR = 0.9, 95% CI = 0.5 to 1.4). Planned observation was associated with significantly lower cranial CT use in patients at intermediate risk (adjusted OR = 0.2, 95% CI = 0.2 to 0.3) and high risk (adjusted OR = 0.1, 95% CI = 0.0 to 0.1) for ciTBI. Conclusions: Even in a setting with low overall cranial CT rates in children with minor head trauma, planned observation was associated with decreased cranial CT use. This strategy can be safely implemented on selected patients in the PECARN intermediate- and higher-risk groups for ciTBI.