Objective: The aim of this study was to compare patient-specific radiobiological parameters with population averages in predicting the clinical outcome after radiotherapy (RT) using a tumour control probability (TCP) model based on the biological effective dose (BED).Methods: A previously published study of 46 head and neck carcinomas with individually identified radiobiological parameters, radiosensitivity and potential doubling time (T pot ), and known tumour size was investigated. These patients had all been treated with external beam RT, and the majority had also received brachytherapy. The TCP for each individual based on the BED using patient-specific radiobiological parameters was compared with the TCP based on the BED using average radiobiological parameters (a50.3 Gy 21 , T pot 53 days).Results: 43 patients remained in the final analysis. There was only a weak trend for increasing local tumour control with increasing BED in both groups. However, when the TCP was calculated, the use of patientspecific parameters was better for identifying local control correctly. The sensitivity and specificity for tumour-specific parameters