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Purpose: To independently and externally validate the Brain Tumour Reporting and Data System (BT-RADS) for post-treatment gliomas and assess interobserver variability. Material and methods: In this retrospective observational study, consecutive MRIs of 100 post-treatment glioma patients were reviewed by two independent radiologists (RD1 and RD2) and assigned a BT-RADS score. Inter-observer agreement statistics were determined by kappa statistics. The BT-RADS-linked management recommendations per score were compared with the multidisciplinary meeting (MDM) decisions. Results: The overall agreement rate between RD1 and RD2 was 62.7% (k = 0.67). The agreement rate between RD1 and consensus was 83.3% (k = 0.85), while the agreement between RD2 and consensus was 69.3% (k = 0.79). Among the radiologists, agreement was highest for score 2 and lowest for score 3b. There was a 97.9% agreement between BT-RADS-linked management recommendations and MDM decisions. Conclusions: BT-RADS scoring led to improved consistency, and standardised language in the structured MRI reporting of post-treatment brain tumours. It demonstrated good overall agreement among the reporting radiologists at both extremes; however, variation rates increased in the middle part of the spectrum. The interpretation categories linked to management decisions showed a near-perfect match with MDM decisions.