PURPOSE: A comprehensive classification based on high resolution computed tomography (CT) of the whole craniofacial region was correlated with clinical findings of combined skull base and maxillofacial fractures. MATERIAL AND METHODS: In a study of two clinical centres, 70 patients with such injuries were admitted at the Universities of Basel (n=29) and Uppsala (n=41). Clinical signs (rhinorrhoea, periorbital haematoma and pneumencephalus) and surgical versus conservative treatment were correlated with a cranio-maxillofacial injury severity score (CMF-ISS) calculated from the classification system. Fracture classifications were decided in consensus on the basis of CT and semiautomatic classification software. The classification system defined 3 fracture types (A, B, C), 3 groups (A1, A2, A3), and 3 subgroups (A1.1, A1.2, A1.3) with increasing severity from A1.1 (lowest) to C3.3 (highest). RESULTS: Of 70 patients, 43 were operated upon and 27 conservatively treated. The operated patients had significantly higher severity scores than non-operated. Patients with or without periorbital haematoma do not differ significantly in the severity score. The severity of the CMF-ISS score was significantly associated (two sample T-test P<0.01) with the occurrence of pneumencephalus, rhinorrhoea and treatment approach. CONCLUSION: Based on our present results, this system seems to be clinical useful for operative decisions and interventions.