The aim of this multi-center phase II study was to clarify the clinical benefit of an opioid-based pain control program for head and neck cancer patients during chemoradiotherapy.Head and neck cancer patients who were to receive definitive or postoperative chemoradiotherapy were enrolled. The opioid-based pain control program consisted of a three-step ladder, with basic regimens of:Step 1: acetaminophen at 500–1000mg three times a day.Step 2: fast-acting morphine at 5mg three times a day before meals for a single day.Step 3: long-acting morphine administered around-the-clock, with a starting dosage of 20mg/day and no upper limit set in principle.The primary endpoint of this study was compliance with radiotherapy.A total of 101 patients from 10 institutions were registered between February 2008 and May 2009 and included in the analysis. The major combination chemotherapy regimen was cisplatin alone (76%). The rate of completion of radiotherapy was 99% and the rate of unplanned breaks in radiotherapy was 13% (13/101, 90% confidence interval: 9.9–16.5%). Median maximum quantity of morphine used per day was 35mg (range 0–150mg).Use of a systematic pain control program may improve compliance with CRT.