Pain is frequent in the course of cancer and can have negative consequences on patients quality of life. The great majority of patients can be helped by simple treatments. The prescription of morphine (M) must be preceded by some explanations. In order to verify the reality of these explanations, a study was done in a 230 comprehensive beds Cancer Centre, with 129 patients, randomized between all the patients hospitalized. In an open questionnaire, different aspects were studied. One hundred answers were studied: 63 patients did not have M at any time: group M – ; 37 patients had M (19) or have had M (18): group M + ; 97% of the patients in group M + thought that M decreased pain, for 85% patients in group M –. Morphine treatment was effective in 92% of patients M +, and not very effective in 5%; 67% of patients M – thought than M is efficient, but 17% did not know; 76% of patients M + did not worry about M; 13% worried et 11% did not know. For patients M – only 48% did not worry; 41% worried and 11% did not know. The side effect known by the patients, and spontaneously quoted were constipation (12 patients in M + group). For 14 patients there was no problem and 2 did not know. In M – group 49 patients did not know. Only 8% of M + group were afraid by addiction, but 44% in group M –; 97% patients M + said that they could stop without problem against only 38% of the patients in M – group. For 16% of M + group, the use of M had a bad signification about their disease, but 52% of M – group thought that if morphine was used in their cases, the meaning would be very bad. The differences between the two groups allow to think that the prescription of M in this study is explained, and that the patients receiving M are rather well informed. Patients with cancer but without M do not have good information and their knowledge is similar than general population. The use of recommanded therapy and explanations allowed patients with M therapy to be confortable with this prescription.