The objective of this study was to develop and validate a French-language questionnaire measuring stereotypes related to exercise in cancer patients: The Cancer Exercise Stereotypes Scale (CESS). Four successive steps were carried out with 806 participants. First, a preliminary version was developed on the basis of the relevant literature and qualitative interviews. A test of clarity then led to the reformulation of six of the 30 items. Second, based on the modification indices of the first confirmatory factorial analysis, 11 of the 30 initial items were deleted. A new factorial structure analysis showed a good fit and validated a 19-item instrument with five subscales. Third, the stability of the instrument was tested over time. Last, tests of construct validity were conducted to examine convergent validity and discriminant validity. The French-language CESS appears to have good psychometric qualities and can be used to test theoretical tenets and inform intervention strategies on ways to foster exercise in cancer patients.