Background and purpose A variety of radiotherapy fractionations are used as potentially curative treatments for non-small cell lung cancer. In the UK, 55 Gy in 20 fractions over 4 weeks (55/20) is the most commonly used fractionation schedule, though it has not been validated in randomized phase III trials. This audit pooled together existing data from 4 UK centres to produce the largest published series for this schedule. Materials and methods 4 UK centres contributed data (Cambridge, Cardiff, Glasgow and Sheffield). Case notes and radiotherapy records of radically treated patients between 1999 and 2007 were retrospectively reviewed. Basic patient demographics, tumour characteristics, radiotherapy and survival data were collected and analysed. Results 609 patients were identified of whom 98% received the prescribed dose of 55/20. The median age was 71.3 years, 62% were male. 90% had histologically confirmed NSCLC, 49% had stage I disease. 27% had received chemotherapy (concurrent or sequential) with their radiotherapy. The median overall survival from time of diagnosis was 24.0 months and 2 year overall survival was 50%. Conclusion These data show respectable results for patients treated with accelerated hypo-fractionated radiotherapy for NSCLC with outcomes comparable to those reported for similar schedules and represent the largest published series to date for 55/20 regime.