To evaluate the clinical benefits of switching from morphine to oral methadone in patients who experience poor analgesia or adverse effects from morphine. Fifty-two consecutive cancer patients receiving oral morphine but with uncontrolled pain and/or moderate to severe opioid adverse effects were switched to oral methadone administered every 8 hours using different dose ratios. Intensity of pain and adverse effects were assessed daily, and the symptom distress score (DS) was calculated before and after switching. Data were analyzed for 50 patients. Switching was considered effective in 80% of the patients; results were achieved in an average of 3.65 days. In the 10 patients who switched to methadone because of uncontrolled pain, a significant reduction in pain intensity (P <.005) and an average of a 33% increase in methadone doses necessary (P <.01) were found after an average of 3.5 days. DS significantly decreased from an average of 8.4 to 4.5 (P <.0005). In the 32 patients switching because of uncontrolled pain and morphine-related adverse effects, significant improvement was found in pain intensity (P <.0005), nausea and vomiting (P <.03), constipation (P <.001), and drowsiness (P <.01), but a significant increase in the methadone dose of an average of 20% (P <.004) was required. In most patients with cancer pain referred for poor pain control and/or adverse effects, switching to oral methadone is a valid therapeutic option. In the clinical setting of poor pain control, higher doses of methadone are necessary with respect to the equianalgesic calculated dose ratios previously published.