What is known and Objective: Bone-cancer pain is a common and refractory cancer pain. Opioids, on their own, do not control this type of pain well enough, and co-analgesics are necessary. Methods: Patients with bone metastasis-related pain at Numeric Rating Scale 4 were enrolled to this randomized placebo-controlled trial. They had also received morphine or transdermal fentanyl patches for at least 1 week. During the 3-day efficacy phase, patients received placebo or 1-3 tablets of oxycodone/paracetamol (5/325 mg), four times daily for 3 days. All patients kept a daily pain diary. The primary endpoint was the Pain Intensity Difference (PID). Secondary endpoints were cases of breakthrough pain and rescue morphine consumption. Additional analyses included the Short Form-6 Dimensions (SF-6D) quality-of-life scale and a general impression (GI) of patient satisfaction with treatment at the end of the phase. Results and Discussion: Of the 246 patients in the intent-to-treat set, 89.4% completed the 3-day efficacy phase. PIDs were 0.9 and 0.3 in the oxycodone/paracetamol and placebo groups respectively, on day 1 (P < 0.001), and 1.5 and 0.3 respectively on day 3 (P < 0.001). Thirty-eight patients in the treatment group, and 58 in the placebo group, suffered breakthrough pain on day 3 (P < 0.001). The SF-6D score decreased to 21.2 +/- 2.5 in the oxycodone/paracetamol group at the end of the phase (P = 0.001). In the oxycodone/paracetamol group, 67% rated GI as good, very good, or excellent. What is new and Conclusion: Patients with bone-cancer pain, already on opioids, obtain clinically important, additional pain-control, with regular oxycodone/paracetamol dosing.