Background: Current guidelines for initial management of traumatic brain injury (TBI) support decision making, but they are rarely validated. The Scandinavian guideline for management of children with TBI (SNC16) was developed to minimise the use of cranial computed tomography (cCT) without compromising safety, but the performance of the guideline in a real-world population is unknown. We aimed to determine the diagnostic accuracy for the SNC16 in a large, pragmatic cohort of children. Methods: In this prospective, observational, international cohort study in 16 Swedish and Norwegian emergency departments (EDs), children (aged <18 years) with blunt head trauma, presenting within 24 h of injury and a Glasgow Coma Scale of 9–15, were prospectively enrolled. The primary outcome measure was presence of a composite variable (clinically important intracranial injury (CIII) comprised of death, neurosurgery, admission to hospital ward ≥2 days due to head injury, or intubation ≥1 day due to pathological cCT findings), all within one week from trauma. Secondary outcome measures were neurosurgery and significant trauma related findings on cCT. Findings: A total of 3012 children were enrolled from April 2018 to May 2024. Nine patients fulfilled the primary variable CIII (0.30%; 9/3012), two patients required neurosurgery (0.07%; 2/3012), and 27 patients showed significant trauma related findings on cCT (0.90%; 27/3012). Point sensitivities to detect CIII, neurosurgery and significant cCT findings were 100% (CI 95% 70%–100% [9/9]; 34%–100% [2/2]; and 87%–100% [27/27]). Point specificity was 41.3%, 41.2%, and 41.6% (CI 95% 40%–43% [1241/3003]; 39%–43% [1241/3010]; and 40%–43% [1241/2985]). Negative predictive values were 100% for CIII, neurosurgery and significant cCT findings (CI 95% 99.7%–100.0% for all). Application of the SNC16 guidelines would have resulted in a mandatory cCT rate of 3.4% (101/3012) and immediate discharge from the ED for 41.2% (1241/3012) of children. No children with a discharge recommendation were positive for any primary or secondary outcomes. Interpretation: Validation of the SNC16 guideline showed adequate diagnostic performance in a real-world cohort, supporting formal implementation. Funding: Non-commercially (Swedish state) funded by Sӧdra Sjukvårdsregionen and Vetenskapliga Rådet, Hallands Hospital and Forskning och Utveckling, Halland. © 2025 The Author(s)