Patients' and caregivers' fear of addiction to and concern about side effects of morphine have been found to be among the major barriers to adequate pain relief in cancer patients. In contrast, the transdermal administration of opioids by means of fentanyl patches does not seem to evoke such fears. In a qualitative study, 60 patients in our outpatient pain clinic recorded up to five associations with a list of diseases, drugs and administration routes. Cancer and AIDS were associated most often with death, followed by suffering, anxiety and hopelessness. Migraine was associated predominantly with pain and other physical symptoms. Aspirin was associated less with pain in general than with headache and, sometimes, specifically with alcohol or hangover. Morphine was associated predominantly with pain and pain relief, but fears of intoxication, abuse and addiction and concerns about side effects were frequently named. Major differences were evident from the associations with the different routes of administration. The word 'pill' was mostly associated with contraception. Associations with 'tablets' were more pharmacological in nature, and side effects were frequently named. Patches were associated with wounds, cuts, bruises, and blisters and with protection. Some associations with patches were related to comfort. Injections and infusions were associated with physicians or the hospital environment. In conclusion, patients expressed major differences in their perceptions of the different drugs and routes of administration. The results may give a first hint that minor cultural differences even between western European countries may lead to major differences in prescribing habits and treatment regimens.