Panobinostat is a radiosensitizing agent and targets the epigenetics of malignancy. This phase I study evaluated the safety and efficacy of combining oral panobinostat with radiotherapy (RT) or chemoradiotherapy (CRT) in patients with inoperable stage III non-small-cell lung cancer. This study had a parallel dose-escalating design combining oral panobinostat twice a week (dose escalations 20, 30, 45 mg) with either palliative RT (group A) or radical CRT (group B) using a standard chemotherapy protocol of cisplatin and etoposide. In group A (RT), nine recruited patients received treatment with oral panobinostat (doses 20, 30, 45 mg) with RT. Two serious adverse events, rapid atrial fibrillation and tracheo-oesophageal fistula, were not attributable to study treatment. The most common grade 3/4 toxicities were thrombocytopenia and lymphopenia, which resolved promptly after cessation of panobinostat. The disease control rate was 66%, the progression-free survival was 3 months and the median overall survival was 9 months. In group B (CRT), panobinostat dose was not escalated beyond 20 mg because of infection-related complications. Serious adverse events included opportunistic infection associated with treatment-related lymphopenia and febrile neutropenia without a source. One patient had cerebral infarct that was not attributed to study treatment. All patients achieved a partial response to treatment. At 33 months of follow-up, all patients were still alive. Panobinostat can be combined with palliative-dose RT at doses up to 45 mg twice a week with tolerable toxicity. Dose-limiting toxicities prevented the dose escalation of the panobinostat with CRT.