Purpose: No randomized studies are available on the additional value of endobronchial brachytherapy (EBB) to external irradiation (XRT) regarding palliation of respiratory symptoms (RS). A prospective randomized study was initiated to test the hypothesis that the addition of EBB to XRT provides higher levels of palliation of dyspnea and other RS and improvement of quality of life (QoL) in patients with non-small cell lung cancer (NSCLC) with endobronchial tumour. Materials and methods: Patients with previously untreated NSCLC, stages I-IIIb, WHO-performance status of 0-3 and with biopsy proven endobronchial tumour in the proximal airways were eligible. EBB consisted of two fractions of 7.5 Gy at 1 cm on day 1 and 8. XRT started at day 2. The XRT dose was 30 Gy (2 weeks) or 60 Gy (6 weeks). The EORTC QLQ-C30 and QLQ-LC13 were assessed before treatment and 2 weeks, 6 weeks, 3, 6 and 12 months after treatment. Re-expansion of collapsed lung was tested by the inspiratory vital capacity (IVC) and CT scan of the chest. Results: Ninety-five patients were randomized between arm 1 (XRT alone) (n = 48) or arm 2 (XRT + EBB) (n = 47). The arms were well balanced regarding pre-treatment characteristics and QoL scores. The compliance for QoL-assessment was >90% at all times. No significant difference between the trial arms was observed with respect to response of dyspnea. However, a beneficial effect of EBB was noted concerning the mean scores of dyspnea over time (P = 0.02), which lasted for 3 months. This benefit was only observed among patients with an obstructing tumour of the main bronchus. A higher rate of re-expansion of collapsed lung was observed in arm 2 (57%) compared to arm 1 (35%) (P = 0.01). The inspiratory vital capacity (IVC) assessed 2 weeks after radiotherapy improved with 493 cm(3) in arm 2 and decreased 50 cm(3) in arm 1 (P = 0.03). No difference was noted regarding the incidence of massive haemoptysis (13 vs. 15%). Conclusion: The addition of EBB to XRT in NSCLC is safe and provides higher rates of re-expansion of collapsed lung resulting in a transient lower levels of dyspnea. This beneficial effect was only observed among patients with obstructing tumours in the main bronchus.