OBJECTIVE Inadequate postoperative pain control remains a problem for many patients undergoing surgery. This study presents subgroup analyses from a large, randomized, multicentre, European study comparing the efficacy and safety of the fentanyl HCl iontophoretic transdermal system and morphine intravenous patient-controlled analgesia for postoperative pain management. METHODS The efficacy and safety of the fentanyl iontophoretic transdermal system and morphine intravenous patient-controlled analgesia were evaluated for patients divided by surgery type, sex, American Society of Anesthesiologists physical status and type of anaesthesia used during surgery. Efficacy measures included a patient global assessment of the method of pain control (a rating of 'good' or 'excellent' was considered as a success rating) and mean last pain intensity scores in the first 24 h. Discontinuation rates and the incidence of adverse events were also evaluated. RESULTS Numerically similar percentages of patients in most subgroups reported success on the last patient global assessment in the first 24 h for both the fentanyl iontophoretic transdermal system and morphine intravenous patient-controlled analgesia. Similar percentages of investigators reported success ratings on the investigator global assessment at the last assessment for both treatment groups regardless of surgery type, except for the knee surgery subgroup (fentanyl iontophoretic transdermal system, 75%; morphine intravenous patient-controlled analgesia, 95%). Mean last pain intensity scores in the first 24 h after surgery were similar in all subgroups. Rates of patient withdrawals and the incidence of adverse events were generally similar between treatment groups in the patient subgroups. CONCLUSIONS The fentanyl iontophoretic transdermal system and morphine intravenous patient-controlled analgesia are comparably well tolerated and effective methods of pain control, regardless of sex, American Society of Anesthesiologists physical status or the type of anaesthesia used for surgery, and following most surgery types.