The aim of this study was to investigate the relationship between standardised uptake value (SUV) obtained from [18F]fluorodeoxyglucose positron emission tomography (FDG PET) and treatment response/survival of inoperable non-small cell lung cancer (NSCLC) patients treated with high dose radiotherapy. Fifty-one patients were included recording stage, performance, weight loss, tumour volume, histology, lymph node involvement, SUV, and delivered radiation dose. The maximum SUV (SUVmax) within the primary tumour was a sensitive and specific factor for predicting treatment response. Apart from SUVmax, stage and performance were also independent predictive factors for treatment response. In a multivariate disease-specific survival (DSS) analysis, SUVmax (P = 0.01), performance status (P = 0.008) and stage (P = 0.04) were prognostic factors. For overall survival (OS), SUVmax (P = 0.001) and performance (P = 0.06) were important prognostic factors. SUVmax was an important prognostic factor for survival of inoperable NSCLC patients and a predictive factor for treatment response. Although the number of patients was small, the treatment was not homogeneous and the use of FDG SUV may have had constraints, we still conclude that the FDG SUV is potentially a good indicator for selecting patients for different treatment strategies.