More than three-quarters of patients questioned said they had experienced pain as a result of drugs or surgery for cancer.
However, fewer than half had been told to expect this by a GP or nurse, and only one in ten had been given any written material on techniques for pain control.
Adequate pain relief is generally thought to be possible in nine out of 10 cancer cases, but most patients were unaware of two key ways of doing this - pain relieving skin patches, and suppositories containing drugs.
The survey was conducted on behalf of Cancer BACUP, a charity which provides information and support to cancer patients.
Its chairman, Maurice Slevin, said: "Pain medication can significantly affect a patient's quality of life and this must be taken into account by all concerned.
"Doctors and patients need to look at and consider the full range of pain medications."
Champion jockey
Cancer BACUP is launching the National Pain Relief Campaign, fronted by former jockey Bob Champion, who beat cancer to ride Aldaniti to victory in the Grand National.
Dr John Ellershaw, a consultant in Palliative Medicine at the Royal Liverpool University Hospital, said: "It is worrying that so many cancer patients seem unaware that it is reasonable for them to ask their doctors for the appropriate drugs to relieve their pain.
"What is even more worrying is that it appears that so many patients actually need to do this."
The campaign is accompanied by a patient information leaflet, "Freedom from Pain", which spells out exactly what sorts of pain relief are available to patients.
Drugs available to help cancer patients range from over-the-counter medications such as paracetamol and aspirin, although patients should check in case they interfere with cancer treatments.
Stronger painkillers, such as higher doses of codeine, are available on prescription.
Finally, doses of morphine and diamorphine can be taken in tablet, syrup or suppository form to relieve severe cancer pain.
Despite these opiates being essentially purer forms of street drugs such as heroin, there is little chance of a strong, physical addiction developing.