An uncontrolled retrospective study was conducted looking at the use of oral controlled-release hydromorphone in palliative care patients. Over a 2-year period 55 patients were switched to hydromorphone therapy, and the efficacy and outcomes were assessed. Urea and electrolyte measurements were also recorded at the time of opioid switch and renal impairment defined as urea > 10.5 mmol/l and/or creatinine > or = 101 mmol/l. This group of 29 patients with abnormal urea and/or creatinine (Group 1) was compared with the remaining 26 patients (Group 2) who had normal urea and creatinine. The major reasons for change to hydromorphone were side-effects (cognitive/drowsiness/nausea) on previous therapy. Following a switch to hydromorphone these side-effects improved in over 80% of patients (n = 55). Comparison between Group 1 and 2 demonstrated a significant difference in renal function but no significant differences in reasons for change, dose of opioids or response to change (over 80% improvement following opioid switch). We conclude that hydromorphone is a flexible second-line alternative to morphine that is particularly useful when intolerable side-effects are experienced with other opioids. In renal impairment (including two patients with end-stage renal failure) we found hydromorphone to be safe and effective. Further clinical and pharmacokinetic studies are required.