PURPOSE: Both the Glasgow Coma Scale (GCS) and Abbreviated Injury Scale (AIS) for head injuries quantify traumatic brain injury (TBI) severity. The GCS is based on brain physiology of consciousness, whereas the AIS is an anatomical injury scoring system. This study aimed to describe the correlation of GCS with maximal AIS-Head (maxAIS) and summative AIS-Head (sumAIS) in TBI patients. METHODS: Data of 4996 adult TBI patients admitted to two level 1 trauma centers in the Netherlands between 2015 and 2021 were selected from the regional trauma registry. The association of GCS with maxAIS and sumAIS was quantified using Spearman rank correlation coefficients (r). RESULTS: For 39% of the patients, the GCS was not documented in the trauma registry. These patients had less severe head injuries than the 3051 patients with documented GCS scores, who were further analyzed. Among those with severe head injuries (AIS-Head ≥ 4), 53% had a GCS score ≥ 13. The GCS showed a weak inverse relationship with both maxAIS and sumAIS (r -0.33 and - 0.34, respectively, both p < 0.001). CONCLUSIONS: The correlation between physiological alterations (GCS) and anatomical brain damage (AIS) in patients with TBI patients, represented by the GCS and AIS respectively, is weak. Additionally, the GCS appears to underestimate the severity of AIS coded severe TBI. Recognizing this limited correlation is important for valid TBI research.